drm/i915/psr: vfunc for disabling source.

VLV/CHV has a total different PSR implementation than the
other platforms, so let's start moving that to vfuncs.
Let's start with disable_src one.

v2: Rebased on top of commit d2419ffc ("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/20170907230041.22978-3-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1180,6 +1180,9 @@ struct i915_psr {
 	bool y_cord_support;
 	bool colorimetry_support;
 	bool alpm;
+
+	void (*disable_source)(struct intel_dp *,
+			       const struct intel_crtc_state *);
 };
 
 enum intel_pch {

drivers/gpu/drm/i915/intel_psr.c

@@ -685,11 +685,7 @@ void intel_psr_disable(struct intel_dp *intel_dp,
 		return;
 	}
 
-	/* Disable PSR on Source */
-	if (HAS_DDI(dev_priv))
-		hsw_psr_disable(intel_dp, old_crtc_state);
-	else
-		vlv_psr_disable(intel_dp, old_crtc_state);
+	dev_priv->psr.disable_source(intel_dp, old_crtc_state);
 
 	/* Disable PSR on Sink */
 	drm_dp_dpcd_writeb(&intel_dp->aux, DP_PSR_EN_CFG, 0);
@@ -987,4 +983,10 @@ void intel_psr_init(struct drm_i915_private *dev_priv)
 
 	INIT_DELAYED_WORK(&dev_priv->psr.work, intel_psr_work);
 	mutex_init(&dev_priv->psr.lock);
+
+	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
+		dev_priv->psr.disable_source = vlv_psr_disable;
+	} else {
+		dev_priv->psr.disable_source = hsw_psr_disable;
+	}
 }