gma500: display displaced vertically by a few lines

[Holger Schurig]

Thanks, Anisse, but Dave's answer was wrong anyway. Using a different
user-space-driver wouldn't have magically fixed the bug in the kernel
KMS driver part.

Eventually something newer will pop up in Debian SID and/or Debian
Backports. I'll then pick it. As the performance of the device doesn't
bother me, I see no need. The more I stay at what Debian provides, the
less I have to maintain by myself :-)