xfree86: Let xf86RandR12CrtcComputeGamma() deal with non-power-of-2 sizes.
The assumption in the upsampling code was that the crtc->gamma_size size of the crtc's gamma table is a power of two. This is true for almost all current driver + gpu combos at least on Linux, with typical sizes of 256, 512, 1024 or 4096 slots. However, Intel Gen-11 Icelake and later are outliers, as their gamma table has 2^18 + 1 slots, very big and not a power of two! Try to make upsampling behave at least reasonable: Replicate the last gamma value to fill up remaining crtc->gamma_red/green/blue slots, which would normally stay uninitialized. This is important, because while the intel display driver does not actually use all 2^18+1 values passed as part of a GAMMA_LUT, it does need the very last slot, which would not get initialized by the old code. This should hopefully create reasonable behaviour with Icelake+ but is untested on the actual Intel hw due to lack of suitable hw. Signed-off-by: Mario Kleiner <firstname.lastname@example.org>