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_socket4_5.c

@@ -28,6 +28,7 @@
 #include <86box/pci.h>
 #include <86box/device.h>
 #include <86box/chipset.h>
+#include <86box/fdc_ext.h>
 #include <86box/hdc.h>
 #include <86box/hdc_ide.h>
 #include <86box/timer.h>
@@ -98,7 +99,10 @@ machine_at_award_common_init(const machine_t *model)
     pci_register_slot(0x06, PCI_CARD_NORMAL, 4, 1, 2, 3);	/* 06 = Slot 4 */
     pci_register_slot(0x07, PCI_CARD_SCSI, 1, 2, 3, 4);		/* 07 = SCSI */
     pci_register_slot(0x02, PCI_CARD_SOUTHBRIDGE, 0, 0, 0, 0);
+
+    if (fdc_type == FDC_INTERNAL)
     device_add(&fdc_at_device);
+
     device_add(&keyboard_ps2_pci_device);
 }