r600g: put radeon_winsys in screen::winsys, don't include drm_driver in the pipe

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/src/gallium/winsys/r600/drm/r600_priv.h b/src/gallium/winsys/r600/drm/r600_priv.h
index 08a3552..8296aa1 100644
--- a/src/gallium/winsys/r600/drm/r600_priv.h
+++ b/src/gallium/winsys/r600/drm/r600_priv.h
@@ -38,6 +38,7 @@
 struct r600_bo;
 
 struct radeon {
+	struct radeon_winsys		*ws;
 	struct radeon_info		info;
 	unsigned			family;
 	enum chip_class			chip_class;