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

[Marcin Kościelnicki]

> 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.

These constants come from nouveau_class.h, which is part of libdrm. Please 
update your libdrm package to the latest git.