drm/radeon/kms: add support for DCE5 display LUTs

The hardware supports advanced user defined color management
but at the moment, there is no infrastructure in place to take
advantage of it so for now we just support the legacy LUTs.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>