drm/amd/display: Add KUnit tests for amdgpu_dm_colorop

drm/amd/display: Add KUnit tests for amdgpu_dm_colorop

[Why & How]
Add a KUnit pipeline test for amdgpu_dm_build_default_pipeline().

The pipeline test uses a mock drm_device (via DRM KUnit helpers),
calls amdgpu_dm_build_default_pipeline() with hw_3d_lut=true, then
walks the returned colorop chain asserting the correct type sequence
(degam_tf, mult, ctm, shaper_tf, shaper_lut, 3dlut, blnd_tf,
blnd_lut), that every op carries bypass_property, and that the
chain length is exactly eight. A kunit cleanup action calls
drm_colorop_pipeline_destroy() before the device is torn down.

Assisted-by: Copilot:Claude-Sonnet-4.6
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>