fix merge botch -- at least compiles now.

merge mga 2.0.0 and r128 6.12.0 drivers.

- implement UploadToScreen() using host blits
- implement DownloadFromScreen() with memcpy() but sync the engine first
- call exaMarkSync() when needed
- don't set EXA_OFFSCREEN_ALIGN_POT unless we actually do xrender acceleration

initial import of xf86-video-r128-6.9.1