dm: treewide: Rename ..._platdata variables to just ..._plat

Try to maintain some consistency between these variables by using _plat as
a suffix for them.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/fs_loader.h

@@ -31,7 +31,7 @@ struct phandle_part {
  * @mtdpart: MTD partition for ubi partition.
  * @ubivol: UBI volume-name for ubifsmount.
  */
-struct device_platdata {
+struct device_plat {
 	struct phandle_part phandlepart;
 	char *mtdpart;
 	char *ubivol;