drm/amd/display: Properly define DPCS related info for DCN301

[Why]
DPCS related info needs to be properly defined within code.

[How]
Add missing DPCS related info to code.

Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Nikola Cornij <nikola.cornij@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>