drm/vboxvideo: Convert vboxvideo driver to |struct drm_gem_vram_object|

This patch replaces |struct vbox_bo| and its helpers with the generic
implementation of |struct drm_gem_vram_object|. The only change in
semantics is that &ttm_bo_driver.verify_access() now does the actual
verification.

v4:
	* select config option DRM_VRAM_HELPER
v3:
	* remove forward declaration of struct vbox_gem_object
v2:
	nothing

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190508082630.15116-18-tzimmermann@suse.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/vboxvideo/vbox_drv.c

@@ -215,9 +215,10 @@ static struct drm_driver driver = {
 	.minor = DRIVER_MINOR,
 	.patchlevel = DRIVER_PATCHLEVEL,
 
-	.gem_free_object_unlocked = vbox_gem_free_object,
+	.gem_free_object_unlocked =
+		drm_gem_vram_driver_gem_free_object_unlocked,
 	.dumb_create = vbox_dumb_create,
-	.dumb_map_offset = vbox_dumb_mmap_offset,
+	.dumb_map_offset = drm_gem_vram_driver_dumb_mmap_offset,
 	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,
 	.prime_fd_to_handle = drm_gem_prime_fd_to_handle,
 	.gem_prime_export = drm_gem_prime_export,