spl: Convert spl_usb_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.c

@@ -400,9 +400,6 @@ static int spl_load_image(u32 boot_device)
 		bootdev.boot_device_name = "usb_ether";
 		return spl_net_load_image(&bootdev);
 #endif
-#ifdef CONFIG_SPL_USB_SUPPORT
-	case BOOT_DEVICE_USB:
-		return spl_usb_load_image(&bootdev);
 #endif
 #ifdef CONFIG_SPL_SATA_SUPPORT
 	case BOOT_DEVICE_SATA:

common/spl/spl_usb.c

@@ -22,7 +22,7 @@ DECLARE_GLOBAL_DATA_PTR;
 static int usb_stor_curr_dev = -1; /* current device */
 #endif
 
-int spl_usb_load_image(struct spl_boot_device *bootdev)
+static int spl_usb_load_image(struct spl_boot_device *bootdev)
 {
 	int err;
 	struct blk_desc *stor_dev;
@@ -61,3 +61,4 @@ int spl_usb_load_image(struct spl_boot_device *bootdev)
 
 	return 0;
 }
+SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_USB, spl_usb_load_image);

include/spl.h

@@ -187,9 +187,6 @@ int spl_spi_load_image(struct spl_boot_device *bootdev);
 /* Ethernet SPL functions */
 int spl_net_load_image(struct spl_boot_device *bootdev);
 
-/* USB SPL functions */
-int spl_usb_load_image(struct spl_boot_device *bootdev);
-
 /* SATA SPL functions */
 int spl_sata_load_image(struct spl_boot_device *bootdev);