spl: Convert spl_spi_load_image() to use linker list

Add a linker list declaration for this method and remove the explicit
switch() code. Also set up the sunxi function.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mtd/spi/sunxi_spi_spl.c b/drivers/mtd/spi/sunxi_spi_spl.c
index 767959c..70d6d15 100644
--- a/drivers/mtd/spi/sunxi_spi_spl.c
+++ b/drivers/mtd/spi/sunxi_spi_spl.c
@@ -262,7 +262,7 @@
 
 /*****************************************************************************/
 
-int spl_spi_load_image(struct spl_boot_device *bootdev)
+static int spl_spi_load_image(struct spl_boot_device *bootdev)
 {
 	int err;
 	struct image_header *header;
@@ -281,3 +281,5 @@
 	spi0_deinit();
 	return 0;
 }
+/* Use priorty 0 to override the default if it happens to be linked in */
+SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_SPI, spl_spi_load_image);