crypto: mediatek - add DT bindings documentation

MediaTek cryptographic accelerators

Required properties:

- compatible: Should be "mediatek,eip97-crypto"

- reg: Address and length of the register set for the device

- interrupts: Should contain the five crypto engines interrupts in numeric

	order. These are global system and four descriptor rings.

- clocks: the clock used by the core

- clock-names: the names of the clock listed in the clocks property. These are

	"ethif", "cryp"

- power-domains: Must contain a reference to the PM domain.

Example:

	crypto: crypto@1b240000 {

		compatible = "mediatek,eip97-crypto";

		reg = <0 0x1b240000 0 0x20000>;

		interrupts = <GIC_SPI 82 IRQ_TYPE_LEVEL_LOW>,

			     <GIC_SPI 83 IRQ_TYPE_LEVEL_LOW>,

			     <GIC_SPI 84 IRQ_TYPE_LEVEL_LOW>,

			     <GIC_SPI 91 IRQ_TYPE_LEVEL_LOW>,

			     <GIC_SPI 97 IRQ_TYPE_LEVEL_LOW>;

		clocks = <&topckgen CLK_TOP_ETHIF_SEL>,

			 <&ethsys CLK_ETHSYS_CRYPTO>;

		clock-names = "ethif","cryp";

		power-domains = <&scpsys MT2701_POWER_DOMAIN_ETH>;

	};