[Nouveau] xf86-video-nouveau compile error and fix

[Martin Wolters]

Hello,

I found xf86-video-nouveau unable to compile on my system. Failing
with two errors in nv_accel_common.c about NV50_2D_CLIP_ENABLE and
NV50_2D_COLOR_KEY_ENABLE not being defined.

Comparing the source to xf86-video-nv, i found the missing constants
to be 0x290 for CLIP_ENABLE and 0x29c for COLOR_KEY_ENABLE. This got
nv_accel_common.c to compile.

I'd request these two constants to be defined to the said values
and this being committed to the git repository.

Regards,
Martin Wolters