[Why]
Enable adaptive scaler support for DCN401

[How]
- Enable build flag for SPL
- Set prefer_easf flag to true
- Apply light linear scaling policy based on transfer function and pixel
  format.  Choose between linear or non-linear scaling
- Set matrix_mode based on pixel format
- Disable ring estimator
- Add missing EASF register defines, masks, and writes
- Disable EASF if scale ratio or number of taps is unsupported and when
  bypassing the scaler
- Add debug flags and registry keys for debugging SPL and EASF
- Add support for Visual Confirm with EASF
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>