drm/amd/powerplay: enable GFX SS for sienna_cichlid

Enable Graphics Clock (GFXCLK) Spread Spectrum for sienna_cichlid.
Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/powerplay/sienna_cichlid_ppt.c

@@ -278,6 +278,7 @@ sienna_cichlid_get_allowed_feature_mask(struct smu_context *smu,
 				| FEATURE_MASK(FEATURE_DS_DCEFCLK_BIT)
 				| FEATURE_MASK(FEATURE_FW_DSTATE_BIT)
 				| FEATURE_MASK(FEATURE_DF_CSTATE_BIT)
+				| FEATURE_MASK(FEATURE_GFX_SS_BIT)
 				| FEATURE_MASK(FEATURE_THERMAL_BIT);
 
 	if (adev->pm.pp_feature & PP_SCLK_DPM_MASK)