RRCrtcGammaSetSize cannot be used yet in xf86InitialConfiguration,
because randr_crtc isn't allocated yet at that point, but a following
change will require RRCrtcGammaSetSize to be called from
xf86RandR12CrtcInitGamma.
v2:
* Bail from xf86RandR12CrtcInitGamma if !crtc->funcs->gamma_set (Keith
Packard)
Reviewed-by: Keith Packard <keithp@keithp.com>