spl: Convert spl_ubi_load_image() to use linker list

Add a linker list declaration for this method and remove the explicit
switch() code.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

common/spl/spl_ubi.c

@@ -76,3 +76,6 @@ out:
 #endif
 	return ret;
 }
+/* Use priorty 0 so that Ubi will override NAND and ONENAND methods */
+SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_NAND, spl_ubi_load_image);
+SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_ONENAND, spl_ubi_load_image);