dt-bindings: mailbox: arm,mhuv3: Add bindings

Add bindings for the ARM MHUv3 Mailbox controller.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

include/dt-bindings/arm/mhuv3-dt.h

+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
+/*
+ * This header provides constants for the defined MHUv3 types.
+ */
+
+#ifndef _DT_BINDINGS_ARM_MHUV3_DT_H
+#define _DT_BINDINGS_ARM_MHUV3_DT_H
+
+#define DBE_EXT		0
+#define FCE_EXT		1
+#define FE_EXT		2
+
+#endif /* _DT_BINDINGS_ARM_MHUV3_DT_H */