Documentation: dt: add bindings for keystone reset driver

* Device tree bindings for Texas Instruments keystone reset

This node is intended to allow SoC reset in case of software reset

of selected watchdogs.

The Keystone SoCs can contain up to 4 watchdog timers to reset

SoC. Each watchdog timer event input is connected to the Reset Mux

block. The Reset Mux block can be configured to cause reset or not.

Additionally soft or hard reset can be configured.

Required properties:

- compatible:		ti,keystone-reset

- ti,syscon-pll:	phandle/offset pair. The phandle to syscon used to

			access pll controller registers and the offset to use

			reset control registers.

- ti,syscon-dev:	phandle/offset pair. The phandle to syscon used to

			access device state control registers and the offset

			in order to use mux block registers for all watchdogs.

Optional properties:

- ti,soft-reset:	Boolean option indicating soft reset.

			By default hard reset is used.

- ti,wdt-list:		WDT list that can cause SoC reset. It's not related

			to WDT driver, it's just needed to enable a SoC related

			reset that's triggered by one of WDTs. The list is

			in format: <0>, <2>; It can be in random order and

			begins from 0 to 3, as keystone can contain up to 4 SoC

			reset watchdogs and can be in random order.

Example 1:

Setup keystone reset so that in case software reset or

WDT0 is triggered it issues hard reset for SoC.

pllctrl: pll-controller@02310000 {

	compatible = "ti,keystone-pllctrl", "syscon";

	reg = <0x02310000 0x200>;

};

devctrl: device-state-control@02620000 {

	compatible = "ti,keystone-devctrl", "syscon";

	reg = <0x02620000 0x1000>;

};

rstctrl: reset-controller {

	compatible = "ti,keystone-reset";

	ti,syscon-pll = <&pllctrl 0xe4>;

	ti,syscon-dev = <&devctrl 0x328>;

	ti,wdt-list = <0>;

};

Example 2:

Setup keystone reset so that in case of software reset or

WDT0 or WDT2 is triggered it issues soft reset for SoC.

rstctrl: reset-controller {

	compatible = "ti,keystone-reset";

	ti,syscon-pll = <&pllctrl 0xe4>;

	ti,syscon-dev = <&devctrl 0x328>;

	ti,wdt-list = <0>, <2>;

	ti,soft-reset;

};