drm/i915: Don't pin the status page as mappable

We access it through the cpu window. No functional difference expected
atm since we default to a bottom-up allocation scheme. But that might
eventually change so that we prefer the unmappable range for buffers
that don't need cpu gtt access.

Split out from Chris vma-bind rework.

Note that this is only possible due to the split-up of the mappable
pin flag into PIN_GLOBAL and PIN_MAPPABLE.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <benjamin.widawsky@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1275,7 +1275,7 @@ static int init_status_page(struct intel_ring_buffer *ring)
 
 	i915_gem_object_set_cache_level(obj, I915_CACHE_LLC);
 
-	ret = i915_gem_obj_ggtt_pin(obj, 4096, PIN_MAPPABLE);
+	ret = i915_gem_obj_ggtt_pin(obj, 4096, 0);
 	if (ret)
 		goto err_unref;