mailbox: arm_mhu: add driver for ARM MHU controller

Add driver for the ARM Primecell Message-Handling-Unit(MHU) controller.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: Andy Green <andy.green@linaro.org>
Signed-off-by: Vincent Yang <vincent.yang@socionext.com>
Signed-off-by: Tetsuya Nuriya <nuriya.tetsuya@socionext.com>
diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
index 84325f2..84b0a2d 100644
--- a/drivers/mailbox/Kconfig
+++ b/drivers/mailbox/Kconfig
@@ -6,6 +6,15 @@
 	  signals. Say Y if your platform supports hardware mailboxes.
 
 if MAILBOX
+
+config ARM_MHU
+	tristate "ARM MHU Mailbox"
+	depends on ARM_AMBA
+	help
+	  Say Y here if you want to build the ARM MHU controller driver.
+	  The controller has 3 mailbox channels, the last of which can be
+	  used in Secure mode only.
+
 config PL320_MBOX
 	bool "ARM PL320 Mailbox"
 	depends on ARM_AMBA