drm/i915: Move GSM mapping into dev_priv

This removes an unused field from the AGP structure and moves it into
the dev_priv structure (with a slightly better name). This builds upon
the kill-agp series already merged.

GSM is a well defined term in the bspec:
GSM: Graphics Stolen Memory

GTT stolen space is defined for storage of the GFX GTT entries in
physical memory. IA can not access GSM directly , it can only access via
GTTMMADR. GT can access GSM directly or through GTTMMADR.

This is not the entire stolen space.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/intel-gtt.h

@@ -18,8 +18,6 @@ struct intel_gtt {
 	/* Share the scratch page dma with ppgtts. */
 	dma_addr_t scratch_page_dma;
 	struct page *scratch_page;
-	/* for ppgtt PDE access */
-	u32 __iomem *gtt;
 	/* needed for ioremap in drm/i915 */
 	phys_addr_t gma_bus_addr;
 } *intel_gtt_get(void);