mailbox: Add Broadcom PDC mailbox driver

The Broadcom PDC mailbox driver is a mailbox controller that
manages data transfers to and from one or more offload engines.

Signed-off-by: Rob Rice <rob.rice@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/Kconfig

@@ -123,4 +123,13 @@ config XGENE_SLIMPRO_MBOX
 	  It is used to send short messages between ARM64-bit cores and
 	  the SLIMpro Management Engine, primarily for PM. Say Y here if you
 	  want to use the APM X-Gene SLIMpro IPCM support.
+
+config BCM_PDC_MBOX
+	tristate "Broadcom PDC Mailbox"
+	depends on ARM64 || COMPILE_TEST
+	default ARCH_BCM_IPROC
+	help
+	  Mailbox implementation for the Broadcom PDC ring manager,
+	  which provides access to various offload engines on Broadcom
+	  SoCs. Say Y here if you want to use the Broadcom PDC.
 endif