drm/amd/display: enable #PME code path for RV.

Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>