imx8: add boot device detection

Add get_boot_device to detect boot device.
Add print_bootinfo to print the boot device info.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Anatolij Gustschin <agust@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/include/asm/arch-imx8/sys_proto.h b/arch/arm/include/asm/arch-imx8/sys_proto.h
new file mode 100644
index 0000000..f9a3016
--- /dev/null
+++ b/arch/arm/include/asm/arch-imx8/sys_proto.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2018 NXP
+ */
+
+#include <asm/mach-imx/sys_proto.h>
+#include <linux/types.h>
+
+enum boot_device get_boot_device(void);
+int print_bootinfo(void);