drm/amd/display: dce_opp: add DCE6 specific macros,functions

drm/amd/display: dce_opp: add DCE6 specific macros,functions

[Why]
DCE6 has no FMT_TRUNCATE_MODE bit in FMT_BIT_DEPTH_CONTROL register
DCE6 has no FMT_CLAMP_COMPONENT_{R,G,B} registers
DCE6 has no FMT_SUBSAMPLING_{MODE,ORDER} bits in FMT_CONTROL register

[How]
Add DCE6 specific macros definitions for OPP registers and masks
DCE6 OPP macros will avoid buiding errors when using DCE6 headers
Add dce60_set_truncation() w/o FMT_TRUNCATE_MODE bit programming
Add dce60_opp_set_clamping() w/o Format Clamp Component programming
Add dce60_opp_program_fmt() w/o Format Subsampling bits programming
Add dce60_opp_program_bit_depth_reduction() with dce60_set_truncation
Use dce60_opp_program_fmt() in dce60_opp_funcs
Use dce60_opp_program_bit_depth_reduction() in dce60_opp_funcs
Add DCE6 specific dce60_opp_construct

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>