drm/amd/display: Create optc.h file

For all the components that participate in DCN architecture, there is a
header in the dc/inch/hw. For some reason, OPTC broke this pattern and
added all the primary functions/structs associated with that in the
dcn10_optc.h file. For consistency's sake, this commit introduces a new
optc.h file and extracts the code from dcn10_optc to this new file.

Reviewed-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Acked-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>