misc: imx: S400_API: Move S400 MU and API to a common place

Since iMX9 uses S401 which shares the API with iMX8ULP. So move S400
MU driver and API to a common place and selected by CONFIG_IMX_SENTINEL

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/include/asm/mach-imx/mu_hal.h b/arch/arm/include/asm/mach-imx/mu_hal.h
new file mode 100644
index 0000000..5db559c
--- /dev/null
+++ b/arch/arm/include/asm/mach-imx/mu_hal.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2021 NXP
+ */
+
+#ifndef __SNT_MU_HAL_H__
+#define __SNT_MU_HAL_H__
+
+void mu_hal_init(ulong base);
+int mu_hal_sendmsg(ulong base, u32 reg_index, u32 msg);
+int mu_hal_receivemsg(ulong base, u32 reg_index, u32 *msg);
+#endif