ati-vga: Fix reverse bit blts

ati-vga: Fix reverse bit blts

The pixman library only supports blts with left to right, top to
bottom order but the ATI VGA engine can also do different directions.
Fix support for these via a temporary buffer for now. This fixes
rendering issues related to such blts (such as moving windows) but
some other glitches still remain.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-id: e21855faaeb30d7b1771f084f283f6a30bedb1a3.1562227303.git.balaton@eik.bme.hu
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>