drm/i915: Handle ENOSPC after failing to insert a mappable node

Even after adding individual page support for GTT mmaping, we can still
fail to find any space within the mappable region, and
drm_mm_insert_node() will then report ENOSPC. We have to then handle
this error by using the shmem access to the pages.

Fixes: b50a53715f09 ("drm/i915: Support for pread/pwrite ... objects")
Testcase: igt/gem_concurrent_blit
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com
Link: http://patchwork.freedesktop.org/patch/msgid/1468690956-23480-1-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -1306,7 +1306,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 		 * textures). Fallback to the shmem path in that case. */
 	}
 
-	if (ret == -EFAULT) {
+	if (ret == -EFAULT || ret == -ENOSPC) {
 		if (obj->phys_handle)
 			ret = i915_gem_phys_pwrite(obj, args, file);
 		else if (i915_gem_object_has_struct_page(obj))