HWRNG support for the iproc-rng200 driver

Required properties:
- compatible : Must be one of:
	       "brcm,bcm7211-rng200"
	       "brcm,bcm7278-rng200"
	       "brcm,iproc-rng200"
- reg : base address and size of control register block

Example:

rng {
        compatible = "brcm,iproc-rng200";
        reg = <0x18032000 0x28>;
};