drm/i915/psr: Add enable_sink vfunc.

Continue on VLV PSR split with vfunc, let's also create one
for enabling sink.

v2: Fix typo on commit message (DK).

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Vathsala Nagaraju <vathsala.nagaraju@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170907230041.22978-11-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1183,6 +1183,7 @@ struct i915_psr {
 
 	void (*disable_source)(struct intel_dp *,
 			       const struct intel_crtc_state *);
+	void (*enable_sink)(struct intel_dp *);
 	void (*activate)(struct intel_dp *);
 	void (*setup_vsc)(struct intel_dp *, const struct intel_crtc_state *);
 };

drivers/gpu/drm/i915/intel_psr.c

@@ -541,17 +541,12 @@ void intel_psr_enable(struct intel_dp *intel_dp,
 	dev_priv->psr.busy_frontbuffer_bits = 0;
 
 	dev_priv->psr.setup_vsc(intel_dp, crtc_state);
+	dev_priv->psr.enable_sink(intel_dp);
 
 	if (HAS_DDI(dev_priv)) {
-		/* Enable PSR on the panel */
-		hsw_psr_enable_sink(intel_dp);
-
 		hsw_psr_enable_source(intel_dp, crtc_state);
 
 	} else {
-		/* Enable PSR on the panel */
-		vlv_psr_enable_sink(intel_dp);
-
 		vlv_psr_enable_source(intel_dp, crtc_state);
 	}
 
@@ -979,10 +974,12 @@ void intel_psr_init(struct drm_i915_private *dev_priv)
 
 	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
 		dev_priv->psr.disable_source = vlv_psr_disable;
+		dev_priv->psr.enable_sink = vlv_psr_enable_sink;
 		dev_priv->psr.activate = vlv_psr_activate;
 		dev_priv->psr.setup_vsc = vlv_psr_setup_vsc;
 	} else {
 		dev_priv->psr.disable_source = hsw_psr_disable;
+		dev_priv->psr.enable_sink = hsw_psr_enable_sink;
 		dev_priv->psr.activate = hsw_psr_activate;
 		dev_priv->psr.setup_vsc = hsw_psr_setup_vsc;
 	}