drm/i915: Use drm_i915_gem_object as the preferred type

A glorified s/obj_priv/obj/ with a net reduction of over a 100 lines and
many characters!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 2565d65..1747e32 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -4,7 +4,7 @@
 struct  intel_hw_status_page {
 	u32	__iomem	*page_addr;
 	unsigned int	gfx_addr;
-	struct		drm_gem_object *obj;
+	struct		drm_i915_gem_object *obj;
 };
 
 #define I915_RING_READ(reg) i915_safe_read(dev_priv, reg)
@@ -32,7 +32,7 @@
 	u32		mmio_base;
 	void		*virtual_start;
 	struct		drm_device *dev;
-	struct		drm_gem_object *gem_object;
+	struct		drm_i915_gem_object *obj;
 
 	unsigned int	head;
 	unsigned int	tail;