drm/amd/display: Fix missing blendTF programming

[Why]
When MPO surface pixel format is not ARGB8888, fast update can miss
programming blendTF.

[How]
Set the gamma_change update flag on blend_tf change.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Ilya Bakoulin <ilya.bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>