various updates to build against xorg-server 21.1.3.

- avoid a const issue with an expanded __UNCONST().
- cope with renamed member names
- deal with "xf86RamDac.h" going away (now use "xf86Cursor.h")

initial import of xf86-video-intel git version 6afed33b2d673d88674f0c76efe500ae414e8e1b

Import the latest from x.org; no improvement over the current screen corruption.

initial import of xf86-video-intel-2.21.15