drm/i915: Save/restore HWS_PGA on suspend/resume

It fixes suspend/resume failure of xf86-video-intel dri2
branch. As dri2 branch doesn't call I830DRIResume() to restore
hardware status page anymore, we need to preserve
this register across suspend/resume.

Signed-off-by: Peng Li <[e-mail]>
Signed-off-by: Eric Anholt <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/i915/i915_drv.h

···
 	u32 saveDSPBCNTR;
 	u32 saveDSPARB;
 	u32 saveRENDERSTANDBY;
+	u32 saveHWS;
 	u32 savePIPEACONF;
 	u32 savePIPEBCONF;
 	u32 savePIPEASRC;

drivers/gpu/drm/i915/i915_suspend.c

···
 	if (IS_I965G(dev) && IS_MOBILE(dev))
 		dev_priv->saveRENDERSTANDBY = I915_READ(MCHBAR_RENDER_STANDBY);
 
+	/* Hardware status page */
+	dev_priv->saveHWS = I915_READ(HWS_PGA);
+
 	/* Display arbitration control */
 	dev_priv->saveDSPARB = I915_READ(DSPARB);
 
···
 	/* Render Standby */
 	if (IS_I965G(dev) && IS_MOBILE(dev))
 		I915_WRITE(MCHBAR_RENDER_STANDBY, dev_priv->saveRENDERSTANDBY);
+
+	/* Hardware status page */
+	I915_WRITE(HWS_PGA, dev_priv->saveHWS);
 
 	/* Display arbitration */
 	I915_WRITE(DSPARB, dev_priv->saveDSPARB);