dt-bindings: hwrng: Add Mediatek hardware random generator bindings

Device-Tree bindings for Mediatek random number generator

found in Mediatek SoC family

Required properties:

- compatible	    : Should be "mediatek,mt7623-rng"

- clocks	    : list of clock specifiers, corresponding to

		      entries in clock-names property;

- clock-names	    : Should contain "rng" entries;

- reg 		    : Specifies base physical address and size of the registers

Example:

rng: rng@1020f000 {

	compatible = "mediatek,mt7623-rng";

	reg = <0 0x1020f000 0 0x1000>;

	clocks = <&infracfg CLK_INFRA_TRNG>;

	clock-names = "rng";

};