drm/amd/display: add plane degamma TF driver-specific property

Allow userspace to tell the kernel driver the input space and,
therefore, uses correct predefined transfer function (TF) to go from
encoded values to linear values.

v2:
- rename TF enum prefix from DRM_ to AMDGPU_ (Harry)
- remove HLG TF

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Joshua Ashton <joshua@froggi.es>
Co-developed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>