drm/i915/psr: Check if VBT says PSR can be enabled.

Driver features data block has a boolean flag for PSR, use this to decide
whether PSR should be enabled on a platform. The module parameter can
still be used to override this.

Note: The feature currently remains disabled by default for all platforms
irrespective of what VBT says.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180509003524.3199-1-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1073,6 +1073,7 @@ struct intel_vbt_data {
 	} edp;
 
 	struct {
+		bool enable;
 		bool full_link;
 		bool require_aux_wakeup;
 		int idle_frames;

drivers/gpu/drm/i915/intel_bios.c

@@ -530,6 +530,7 @@ parse_driver_features(struct drm_i915_private *dev_priv,
 	 */
 	if (!driver->drrs_enabled)
 		dev_priv->vbt.drrs_type = DRRS_NOT_SUPPORTED;
+	dev_priv->vbt.psr.enable = driver->psr_enabled;
 }
 
 static void

drivers/gpu/drm/i915/intel_psr.c

@@ -1173,9 +1173,12 @@ void intel_psr_init(struct drm_i915_private *dev_priv)
 	if (!dev_priv->psr.sink_support)
 		return;
 
+	if (i915_modparams.enable_psr == -1) {
+		i915_modparams.enable_psr = dev_priv->vbt.psr.enable;
+
 		/* Per platform default: all disabled. */
-	if (i915_modparams.enable_psr == -1)
 		i915_modparams.enable_psr = 0;
+	}
 
 	/* Set link_standby x link_off defaults */
 	if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))