spl: Convert spl_onenand_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>
diff --git a/common/spl/spl_onenand.c b/common/spl/spl_onenand.c
index f5e2f95..361a1b3 100644
--- a/common/spl/spl_onenand.c
+++ b/common/spl/spl_onenand.c
@@ -14,7 +14,7 @@
 #include <asm/io.h>
 #include <onenand_uboot.h>
 
-int spl_onenand_load_image(struct spl_boot_device *bootdev)
+static int spl_onenand_load_image(struct spl_boot_device *bootdev)
 {
 	struct image_header *header;
 	int ret;
@@ -34,3 +34,5 @@
 
 	return 0;
 }
+/* Use priorty 1 so that Ubi can override this */
+SPL_LOAD_IMAGE_METHOD(1, BOOT_DEVICE_ONENAND, spl_onenand_load_image);