drm/amd/display: Add DMUB support for DCN316

Initialize DMUB for DCN316. Use same funcs as DCN31 for
DCN316.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Prike Liang <Prike.Liang@amd.com>
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>