Revert "modesetting: Only use GAMMA_LUT if its size is 1024"

This reverts commit 617f591f.

The problem described in that commit exists, but the two
preceeding commits with improvements to the servers RandR
code should avoid the mentioned problems while allowing the
use of GAMMA_LUT's instead of legacy gamma lut.

Use of legacy gamma lut's is not a good fix, because it will reduce
color output precision of gpu's with more than 1024 GAMMA_LUT
slots, e.g., AMD, ARM MALI and KOMEDA with 4096 slot luts,
and some Mediathek parts with 512 slot luts. On KOMEDA, legacy
lut's are completely unsupported by the kms driver, so gamma
correction gets disabled.

The situation is especially bad on Intel Icelake and later:
Use of legacy gamma tables will cause the kms driver to switch
to hardware legacy lut's with 256 slots, 8 bit wide, without
interpolation. This way color output precision is restricted to
8 bpc and any deep color / HDR output (10 bpc, fp16, fixed point 16)
becomes impossible. The latest Intel gen gpu's would have worse
color precision than parts which are more than 10 years old.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>