bcm2835: Add Broadcom VideoCore Mailbox IPC to the device tree

This adds a device tree binding for Mailbox IPC mechanism present on Broadcom
BCM2835 SoC, used in Raspberry Pi and Roku 2 devices.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: linux-rpi-kernel@lists.infradead.org
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
mailbox: Add VideoCore Mailbox IPC driver

This adds a driver for Mailbox IPC mechanism present on Broadcom
BCM2835 SoC, used in Raspberry Pi and Roku 2 devices.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: linux-rpi-kernel@lists.infradead.org