drm/amd/display: dce_transform: DCE6 Scaling Horizontal Filter Init (v2)

[Why]
DCE6 has specific SCL_HORZ_FILTER_INIT_{LUMA_RGB,CHROMA} registers
In DCE6 h_init_luma and h_init_chroma initialization is required
Some DCE6 specific SCL_{HORZ,VERT}_FILTER_CONTROL masks were not listed

[How]
Add the registers and masks in dce_transform.h
Add DCE6 specific struct sclh_ratios_inits in dce_transform.h
Add dce60_calculate_inits() function
Add dce60_program_scl_ratios_inits() function
Fix dce60_transform_set_scaler() function

v2: remove unused variable (Alex)

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mauro Rossi <issor.oruam@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>