dt-bindings: soc: Add a binding for the Broadcom VCHIQ services. (v3)

The VCHIQ communication channel can be provided by BCM283x and Capri
SoCs, to communicate with the VPU-side OS services.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/soc/bcm/brcm,bcm2835-vchiq.txt

+Broadcom VCHIQ firmware services
+
+Required properties:
+
+- compatible:	Should be "brcm,bcm2835-vchiq"
+- reg:		Physical base address and length of the doorbell register pair
+- interrupts:	The interrupt number
+		  See bindings/interrupt-controller/brcm,bcm2835-armctrl-ic.txt
+
+Example:
+
+mailbox@7e00b840 {
+	compatible = "brcm,bcm2835-vchiq";
+	reg = <0x7e00b840 0xf>;
+	interrupts = <0 2>;
+};