drm/amd/display: Update register defines

[Why]
Some register defines are redundant or updated

[How]
Update register defines
Remove some redundant defines

Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Wyatt Wood <Wyatt.Wood@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Sun peng Li <Sunpeng.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>