drm/amd/display: Add fSMC_MSG_SetDtbClk support

[why]
Needed to support dcn315

Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Oliver Logush <oliver.logush@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>