drm/amd/display: DML2.1 changes

* Add a missing compilation unit
* Missing CFLAGS for certain units

Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>