Video changes part 1 for 4.2

1. Corrected the ATI 1881x clocks for use with the ATI Mach8/32 and VGA Wonder chips. The CPU slowdowns should now be gone.
2. Merged I/O ports common to both the ATI and IBM 8514/A compatible chips where they have identical code (extended behavior is still separate). Code duplication is now less than before.
3. Fixed a general polygon pattern issue in the Mach8/32 affecting calc.exe in Win3.x and other stuff.
4. Mode changes are, once again, changed (ATI and IBM), as close as possible to the real thing without destroying existing resolutions.
5. The 8514/A Vertical Counter has been extended to 0xfff so that it can take 1280x1024 resolutions well offered by the Mach32 as well as a better way to change the IBM/ATI modes through a callback swap where approprietate.
6. in 8514/A mode, reads from the 0x3c6-0x3c9 ramdac range is redirected to the 8514/A RAMDAC (0x2ea-0x2ed).
7. LFB access in the Mach32 now no longer takes account of the SVGA derived rops. Fixes Mach32 display on NeXTSTEP/OPENSTEP 3.x/4.x
8. Reworked the Display Sense Status and Subsystem Status ports so that they're not copycats from MAME and instead follow the datasheet.

src/include/86box/vid_ati_mach8.h

@@ -74,6 +74,7 @@ typedef struct mach_t {
     uint16_t shadow_set;
     uint16_t shadow_cntl;
     int ext_on[2];
+    int extended_mode;
     int compat_mode;
 
     struct {