FDC workaround

The Internal FDC is added when needed for AT machines too.
Some speculative "work" on the main FDC code

src/machine/m_at_286_386sx.c

@@ -35,6 +35,7 @@
 #include <86box/rom.h>
 #include <86box/fdd.h>
 #include <86box/fdc.h>
+#include <86box/fdc_ext.h>
 #include <86box/hdc.h>
 #include <86box/sio.h>
 #include <86box/serial.h>
@@ -56,6 +57,8 @@ machine_at_mr286_init(const machine_t *model)
 
     machine_at_common_ide_init(model);
     device_add(&keyboard_at_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     return ret;
@@ -66,6 +69,8 @@ static void
 machine_at_headland_common_init(int ht386)
 {
     device_add(&keyboard_at_ami_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     if (ht386)
@@ -136,7 +141,10 @@ machine_at_quadt286_init(const machine_t *model)
 
     machine_at_common_init(model);
     device_add(&keyboard_at_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
+
     device_add(&headland_gc10x_device);
 
     return ret;
@@ -157,6 +165,8 @@ machine_at_neat_init(const machine_t *model)
     machine_at_init(model);
 
     device_add(&neat_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     return ret;
@@ -177,6 +187,8 @@ machine_at_neat_ami_init(const machine_t *model)
     machine_at_common_init(model);
 
     device_add(&neat_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     device_add(&keyboard_at_ami_device);
@@ -198,7 +210,10 @@ machine_at_px286_init(const machine_t *model)
 
     machine_at_common_init(model);
     device_add(&keyboard_at_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
+
     device_add(&neat_device);
 
     return ret;
@@ -219,6 +234,8 @@ machine_at_micronics386_init(const machine_t *model)
     machine_at_init(model);
 
     device_add(&neat_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     return ret;
@@ -230,6 +247,8 @@ machine_at_scat_init(const machine_t *model, int is_v4)
 {
     machine_at_common_init(model);
     device_add(&keyboard_at_ami_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     if (is_v4)
@@ -245,6 +264,8 @@ machine_at_scatsx_init(const machine_t *model)
     machine_at_common_init(model);
 
     device_add(&keyboard_at_ami_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     device_add(&scat_sx_device);
@@ -434,6 +455,8 @@ machine_at_shuttle386sx_init(const machine_t *model)
 
     device_add(&intel_82335_device);
     device_add(&keyboard_at_ami_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     return ret;
@@ -456,6 +479,8 @@ machine_at_adi386sx_init(const machine_t *model)
 
     device_add(&intel_82335_device);
     device_add(&keyboard_at_ami_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     return ret;
@@ -502,7 +527,10 @@ machine_at_commodore_sl386sx16_init(const machine_t *model)
     machine_at_common_ide_init(model);
 
     device_add(&keyboard_at_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
+
     device_add(&neat_device);
     /* Two serial ports - on the real hardware SL386SX-16, they are on the single UMC UM82C452. */
     device_add_inst(&ns16450_device, 1);
@@ -518,7 +546,10 @@ machine_at_scamp_common_init(const machine_t *model)
     machine_at_common_ide_init(model);
 
     device_add(&keyboard_ps2_ami_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
+
     device_add(&vlsi_scamp_device);
 }
 
@@ -591,6 +622,8 @@ machine_at_awardsx_init(const machine_t *model)
     machine_at_init(model);
 
     device_add(&opti291_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     return ret;
@@ -704,6 +737,8 @@ machine_at_olim290_init(const machine_t *model)
 
     machine_at_common_init(model);
     device_add(&keyboard_at_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
     
     io_sethandler(0x069, 1, m290_read, NULL, NULL, NULL, NULL, NULL, NULL);
@@ -730,6 +765,8 @@ machine_at_ncrpc8_init(const machine_t *model)
 
     machine_at_common_init(model);
     device_add(&keyboard_at_ncr_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
     
     return ret;
@@ -758,6 +795,8 @@ machine_at_ncr3302_init(const machine_t *model)
     machine_at_common_ide_init(model);
     device_add(&neat_device);
     device_add(&keyboard_at_ncr_device);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
 
     if (gfxcard == VID_INTERNAL)