* rWTM BIU Mailbox driver for Armada 37xx

Required properties:
- compatible:	must be "marvell,armada-3700-rwtm-mailbox"
- reg:		physical base address of the mailbox and length of memory mapped
		region
- interrupts:	the IRQ line for the mailbox
- #mbox-cells:	must be 1

Example:
	rwtm: mailbox@b0000 {
		compatible = "marvell,armada-3700-rwtm-mailbox";
		reg = <0xb0000 0x100>;
		interrupts = <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH>;
		#mbox-cells = <1>;
	};