sandbox_spl: Restrict use of UPL when not enabled

With sandbox_spl we want to use the file-based boot in CI, so that this
flow is tested. The recent UPL change enabled booting via that method,
thus overriding the file-based boot.

Correct this by using UPL only when the --upl flag is given.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: 91fde8e1764 ("sandbox: Add an SPL loader for UPL")
diff --git a/arch/sandbox/cpu/spl.c b/arch/sandbox/cpu/spl.c
index c50df5f..7056cfd 100644
--- a/arch/sandbox/cpu/spl.c
+++ b/arch/sandbox/cpu/spl.c
@@ -55,9 +55,10 @@
 
 void board_boot_order(u32 *spl_boot_list)
 {
+	struct sandbox_state *state = state_get_current();
+
 	spl_boot_list[0] = BOOT_DEVICE_VBE;
-	spl_boot_list[1] = BOOT_DEVICE_UPL;
-	spl_boot_list[2] = BOOT_DEVICE_BOARD;
+	spl_boot_list[1] = state->upl ? BOOT_DEVICE_UPL : BOOT_DEVICE_BOARD;
 }
 
 static int spl_board_load_file(struct spl_image_info *spl_image,