drm/nouveau/kms/nv50-: Always validate LUTs in nv50_head_atomic_check_lut()

drm/nouveau/kms/nv50-: Always validate LUTs in nv50_head_atomic_check_lut()

When it comes to gamma or degamma luts, nouveau will actually skip the
calculation of certain LUTs depending on the head and plane states. For
instance, when the head is disabled we don't perform any error checking on
the gamma LUT, and likewise if no planes are present and enabled in our
atomic state we will skip error checking the degamma LUT. This is a bit of
a problem though, since the per-head gamma and degamma props in DRM can be
changed even while a head is disabled - a situation which can be triggered
by the igt testcase mentioned down below.

Originally I thought this was a bit silly and was tempted to just fix the
igt test to only set gamma/degamma with the head enabled. After a bit of
thinking though I realized we should fix this in nouveau. This is because
if a program decides to set an invalid LUT for a head before enabling the
head, such a property change would succeed while also making it impossible
to turn the head back on until the LUT is removed or corrected - something
that could be painful for a user to figure out.

So, fix this checking both degamma and gamma LUTs unconditionally during
atomic checks. We start by calling nv50_head_atomic_check_lut() regardless
of whether the head is active or not in nv50_head_atomic_check(). Then we
move the ilut error checking into nv50_head_atomic_check_lut() and add a
per-head hook for it, primarily because as a per-CRTC property DRM we want
the LUT to be error checked by the head any time it's included in an atomic
state. Of course though, actual programming of the degamma lut to hardware
is still handled in each plane's atomic check and commit.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Testcase: igt/kms_color/pipe-invalid-*-lut-sizes
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/10