drm/gem: Export drm_gem_vmap() and drm_gem_vunmap()

The symbols will be required by the upcoming helpers for shadow-buffered
planes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210208115538.6430-3-tzimmermann@suse.de

drivers/gpu/drm/drm_gem.c

@@ -1212,6 +1212,7 @@ int drm_gem_vmap(struct drm_gem_object *obj, struct dma_buf_map *map)
 
 	return 0;
 }
+EXPORT_SYMBOL(drm_gem_vmap);
 
 void drm_gem_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map)
 {
@@ -1224,6 +1225,7 @@ void drm_gem_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map)
 	/* Always set the mapping to NULL. Callers may rely on this. */
 	dma_buf_map_clear(map);
 }
+EXPORT_SYMBOL(drm_gem_vunmap);
 
 /**
  * drm_gem_lock_reservations - Sets up the ww context and acquires