drm/amd/display: add missing ABM registers

[Why]
We are currently missing some ABM registers.

[How]
Add the missing registers to dce_abm.h.

Reviewed-by: Jun Lei <jun.lei@amd.com>
Reviewed-by: Chris Park <chris.park@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Sridevi Arvindekar <sridevi.arvindekar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>