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>

drivers/gpu/drm/i915/i915_drv.h

@@ -800,6 +800,9 @@ typedef struct drm_i915_private {
 		unsigned long gtt_end;
 		unsigned long stolen_base; /* limited to low memory (32-bit) */
 
+		/** "Graphics Stolen Memory" holds the global PTEs */
+		uint32_t __iomem *gsm;
+
 		struct io_mapping *gtt_mapping;
 		phys_addr_t gtt_base_addr;
 		int gtt_mtrr;