sandbox: Generalise SPL booting

At present sandbox only supports jumping to a file, to get to the next
U-Boot phase. We want to support other methods, so update the code to
use an enum for the method. Also use the

Use board_boot_order() to set the order, so we can add more options.
Also add the MMC methods into the BOOT_DEVICE enum so that booting
from MMC can be supported.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/spl.c b/arch/sandbox/cpu/spl.c
index 9c59cc2..2678370 100644
--- a/arch/sandbox/cpu/spl.c
+++ b/arch/sandbox/cpu/spl.c
@@ -49,13 +49,13 @@
 	preloader_console_init();
 }
 
-u32 spl_boot_device(void)
+void board_boot_order(u32 *spl_boot_list)
 {
-	return BOOT_DEVICE_BOARD;
+	spl_boot_list[0] = BOOT_DEVICE_BOARD;
 }
 
-static int spl_board_load_image(struct spl_image_info *spl_image,
-				struct spl_boot_device *bootdev)
+static int spl_board_load_file(struct spl_image_info *spl_image,
+			       struct spl_boot_device *bootdev)
 {
 	char fname[256];
 	int ret;
@@ -74,10 +74,11 @@
 	if (!spl_image->arg)
 		return log_msg_ret("exec", -ENOMEM);
 	strcpy(spl_image->arg, fname);
+	spl_image->flags = SPL_SANDBOXF_ARG_IS_FNAME;
 
 	return 0;
 }
-SPL_LOAD_IMAGE_METHOD("sandbox", 9, BOOT_DEVICE_BOARD, spl_board_load_image);
+SPL_LOAD_IMAGE_METHOD("sandbox", 9, BOOT_DEVICE_BOARD, spl_board_load_file);
 
 void spl_board_init(void)
 {
@@ -96,13 +97,21 @@
 
 void __noreturn jump_to_image_no_args(struct spl_image_info *spl_image)
 {
-	const char *fname = spl_image->arg;
+	switch (spl_image->flags) {
+	case SPL_SANDBOXF_ARG_IS_FNAME: {
+		const char *fname = spl_image->arg;
 
-	if (fname) {
-		os_fd_restore();
-		os_spl_to_uboot(fname);
-	} else {
-		printf("No filename provided for U-Boot\n");
+		if (fname) {
+			os_fd_restore();
+			os_spl_to_uboot(fname);
+		} else {
+			log_err("No filename provided for U-Boot\n");
+		}
+		break;
+	}
+	default:
+		log_err("Invalid flags\n");
+		break;
 	}
 	hang();
 }