arm: spl: Provide for a board-specific loader

Some boards have a special way of loading U-Boot that does not fit with
the existing SPL code. For example sunxi uses an 'FEL' mode where U-Boot
is loaded over USB. Add a CONFIG option and boot mode for this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

arch/arm/include/asm/spl.h

@@ -26,10 +26,14 @@ enum {
 	BOOT_DEVICE_SPI,
 	BOOT_DEVICE_SATA,
 	BOOT_DEVICE_I2C,
+	BOOT_DEVICE_BOARD,
 	BOOT_DEVICE_NONE
 };
 #endif
 
+/* Board-specific load method */
+void spl_board_load_image(void);
+
 /* Linker symbols. */
 extern char __bss_start[], __bss_end[];
 

common/spl/spl.c

@@ -229,6 +229,11 @@ void board_init_r(gd_t *dummy1, ulong dummy2)
 		spl_sata_load_image();
 		break;
 #endif
+#ifdef CONFIG_SPL_BOARD_LOAD_IMAGE
+	case BOOT_DEVICE_BOARD:
+		spl_board_load_image();
+		break;
+#endif
 	default:
 #if defined(CONFIG_SPL_SERIAL_SUPPORT) && defined(CONFIG_SPL_LIBCOMMON_SUPPORT)
 		puts("SPL: Unsupported Boot Device!\n");