Changes to 8514/A compatible stuff (November 2nd, 2024)

1. vga_on global variable removed, as it didn't play well with 2 subsystems at once (8514/A and XGA both enabled).
2. Emulate the Foreground/Background Color aliases of PIX_TRANS properly when not executing a command.
3. Voodoo 3D override now works properly (again) with Mach32 PCI cards and others by turning the 8514/A timer off and on accordingly.

src/include/86box/vid_8514a.h

@@ -42,7 +42,6 @@ typedef union {
 typedef struct ibm8514_t {
     rom_t bios_rom;
     rom_t bios_rom2;
-    rom_t bios_rom3;
     hwcursor8514_t hwcursor;
     hwcursor8514_t hwcursor_latch;
     uint8_t        pos_regs[8];
@@ -228,6 +227,7 @@ typedef struct ibm8514_t {
     uint32_t vram_amount;
     int      vram_512k_8514;
     PALETTE  _8514pal;
+    int      vendor_mode;
 
     latch8514_t latch;
 } ibm8514_t;