agp/intel-gtt: export the gtt pagetable iomapping

We need this because ppgtt page directory entries need to be in the
global gtt pagetable.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/intel-gtt.h b/include/drm/intel-gtt.h
index 6d4c77a..0a0001b 100644
--- a/include/drm/intel-gtt.h
+++ b/include/drm/intel-gtt.h
@@ -17,6 +17,8 @@
 	unsigned int do_idle_maps : 1;
 	/* Share the scratch page dma with ppgtts. */
 	dma_addr_t scratch_page_dma;
+	/* for ppgtt PDE access */
+	u32 __iomem *gtt;
 } *intel_gtt_get(void);
 
 void intel_gtt_chipset_flush(void);