drm/amd/display: Extract transfer function helpers

drm/amd/display: Extract transfer function helpers

[Why]
Extract repeated inline dc_transfer_func setup patterns into two
small helper functions in amdgpu_dm_color.c.

Three functions (amdgpu_dm_set_atomic_regamma,
amdgpu_dm_atomic_shaper_lut, amdgpu_dm_atomic_blend_lut) each
contained identical two-line bypass setup and identical three-line
distributed-points setup. __set_colorop_in_tf_1d_curve contained
the same two-line bypass pattern as well.

[How]
Extract to __set_tf_bypass() and __set_tf_distributed_points().
Replace all four bypass sites with __set_tf_bypass(), and all three
distributed-points sites with __set_tf_distributed_points().

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>