drm/i915/psr: Add setup VSC vfunc.

Continue on VLV PSR split with vfunc, let's also create
one for setting up VSC.

v2: Rebased on top of commit d2419ffc10e4 ("drm/i915: Plumb
    crtc_state to PSR enable/disable")

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/20170907230041.22978-10-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1184,6 +1184,7 @@ struct i915_psr {
 	void (*disable_source)(struct intel_dp *,
 			       const struct intel_crtc_state *);
 	void (*activate)(struct intel_dp *);
+	void (*setup_vsc)(struct intel_dp *, const struct intel_crtc_state *);
 };
 
 enum intel_pch {

drivers/gpu/drm/i915/intel_psr.c

@@ -540,18 +540,15 @@ void intel_psr_enable(struct intel_dp *intel_dp,
 
 	dev_priv->psr.busy_frontbuffer_bits = 0;
 
-	if (HAS_DDI(dev_priv)) {
-
-		hsw_psr_setup_vsc(intel_dp, crtc_state);
+	dev_priv->psr.setup_vsc(intel_dp, crtc_state);
 
+	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 {
-		vlv_psr_setup_vsc(intel_dp, crtc_state);
-
 		/* Enable PSR on the panel */
 		vlv_psr_enable_sink(intel_dp);
 
@@ -983,8 +980,10 @@ 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.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.activate = hsw_psr_activate;
+		dev_priv->psr.setup_vsc = hsw_psr_setup_vsc;
 	}
 }