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 <peng.li@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b24d522..0a4f39b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -150,6 +150,7 @@
 	u32 saveDSPBCNTR;
 	u32 saveDSPARB;
 	u32 saveRENDERSTANDBY;
+	u32 saveHWS;
 	u32 savePIPEACONF;
 	u32 savePIPEBCONF;
 	u32 savePIPEASRC;