drm/amd/display: Add more color KUnit tests

drm/amd/display: Add more color KUnit tests

[Why & How]
Add KUnit tests for __set_tf_bypass(), __set_tf_distributed_points(),
the bypass paths of amdgpu_dm_set_atomic_regamma(),
amdgpu_dm_atomic_shaper_lut(), and amdgpu_dm_atomic_blend_lut(), and
all three input branches of __set_colorop_in_tf_1d_curve().

Export the three shaper/blend/regamma helpers and
__set_colorop_in_tf_1d_curve with STATIC_IFN_KUNIT and EXPORT_IF_KUNIT
to make their branches reachable from tests.
Add the following test cases in amdgpu_dm_color_test.c:
- dm_test_set_tf_bypass: verify bypass TF setup
- dm_test_set_tf_distributed_points_srgb: validate sRGB gamma
- dm_test_set_tf_distributed_points_pq: validate PQ gamma
- dm_test_set_atomic_regamma_bypass: verify regamma bypass path
- dm_test_atomic_shaper_lut_bypass: verify shaper LUT bypass path
- dm_test_atomic_blend_lut_bypass: verify blend LUT bypass path
- dm_test_set_colorop_in_tf_1d_curve_invalid_type: verify invalid
  colorop type returns -EINVAL
- dm_test_set_colorop_in_tf_1d_curve_unsupported_curve: verify
  unsupported curve type returns -EINVAL
- dm_test_set_colorop_in_tf_1d_curve_bypass: verify bypass path sets
  TF_TYPE_BYPASS and TRANSFER_FUNCTION_LINEAR

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>