imx93: Use a header for imx9_probe_mu declaration

Put imx9_probe_mu declaration in a new mu.h header file.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>
Reviewed-by: Igor Opaniuk <igor.opaniuk@foundries.io>
diff --git a/arch/arm/include/asm/arch-imx9/mu.h b/arch/arm/include/asm/arch-imx9/mu.h
new file mode 100644
index 0000000..b860499
--- /dev/null
+++ b/arch/arm/include/asm/arch-imx9/mu.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2024 Mathieu Othacehe <m.othacehe@gmail.com>
+ */
+
+#ifndef __ARCH_IMX9_MU_H
+#define __ARCH_IMX9_MU_H
+
+#include <event.h>
+
+int imx9_probe_mu(void *ctx, struct event *event);
+
+#endif