Implemented preliminary S3 ViRGE 2D blitter emulation.

Misc ViRGE fixes.
Changes to memory mapping.
Changes to PCI handling.
Disabled 'AMI WinBIOS 486 PCI' due to incomplete chipset emulation.
Invalid GUS register reads no longer kill the emulator.

src/vid_ega.h

@@ -2,6 +2,8 @@ typedef struct ega_t
 {
         mem_mapping_t mapping;
         
+        rom_t bios_rom;
+        
         uint8_t crtcreg;
         uint8_t crtc[32];
         uint8_t gdcreg[16];