drm/i915: Enable eDP DRRS for CHV

This patch enables eDP DRRS for CHV by adding the
required IS_CHERRYVIEW() checks.
CHV uses the same register bit as VLV.

[Vandana]: Since CHV has 2 sets of M_N registers, it will follow the same code
path as gen < 8. Added CHV check in dp_set_m_n()

[Ram]: Rebased on top of previous patch modifications

Signed-off-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -5879,7 +5879,7 @@ static void intel_cpu_transcoder_set_m_n(struct intel_crtc *crtc,
 		 * for gen < 8) and if DRRS is supported (to make sure the
 		 * registers are not unnecessarily accessed).
 		 */
-		if (m2_n2 && INTEL_INFO(dev)->gen < 8 &&
+		if (m2_n2 && (IS_CHERRYVIEW(dev) || INTEL_INFO(dev)->gen < 8) &&
 			crtc->config->has_drrs) {
 			I915_WRITE(PIPE_DATA_M2(transcoder),
 					TU_SIZE(m2_n2->tu) | m2_n2->gmch_m);

drivers/gpu/drm/i915/intel_dp.c

@@ -4808,7 +4808,7 @@ static void intel_dp_set_drrs_state(struct drm_device *dev, int refresh_rate)
 		return;
 	}
 
-	if (INTEL_INFO(dev)->gen >= 8) {
+	if (INTEL_INFO(dev)->gen >= 8 && !IS_CHERRYVIEW(dev)) {
 		switch (index) {
 		case DRRS_HIGH_RR:
 			intel_dp_set_m_n(intel_crtc, M1_N1);