[Backport gnome 40] KMS: Survive missing GAMMA_LUT property

Some KMS driver don't support GAMMA_LUT property. (like mgag200 and ast)

This causes a black screen, and the following errors from gnome-shell:

gnome-shell[5405]: Page flip discarded: drmModeAtomicCommit: Invalid argument

gnome-shell[5405]: Failed to post KMS update: drmModeAtomicCommit: Invalid argument

Fixes: #2197 (closed)

Part-of: !2360 (merged) (cherry picked from commit 364572b9)