spl: Convert spl_nor_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_nor.c b/common/spl/spl_nor.c
index f10d679..b55fcc5 100644
--- a/common/spl/spl_nor.c
+++ b/common/spl/spl_nor.c
@@ -7,7 +7,7 @@
 #include <common.h>
 #include <spl.h>
 
-int spl_nor_load_image(struct spl_boot_device *bootdev)
+static int spl_nor_load_image(struct spl_boot_device *bootdev)
 {
 	int ret;
 	/*
@@ -70,3 +70,4 @@
 
 	return 0;
 }
+SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_NOR, spl_nor_load_image);