Documentation: dt: add bindings for TI Wakeup M3 IPC device

Wakeup M3 IPC Driver

=====================

The TI AM33xx and AM43xx family of devices use a small Cortex M3 co-processor

(commonly referred to as Wakeup M3 or CM3) to help with various low power tasks

that cannot be controlled from the MPU, like suspend/resume and certain deep

C-states for CPU Idle. Once the wkup_m3_ipc driver uses the wkup_m3_rproc driver

to boot the wkup_m3, it handles communication with the CM3 using IPC registers

present in the SoC's control module and a mailbox. The wkup_m3_ipc exposes an

API to allow the SoC PM code to execute specific PM tasks.

Wkup M3 Device Node:

====================

A wkup_m3_ipc device node is used to represent the IPC registers within an

SoC.

Required properties:

--------------------

- compatible:		Should be,

				"ti,am3352-wkup-m3-ipc" for AM33xx SoCs

				"ti,am4372-wkup-m3-ipc" for AM43xx SoCs

- reg:			Contains the IPC register address space to communicate

			with the Wakeup M3 processor

- interrupts:		Contains the interrupt information for the wkup_m3

			interrupt that signals the MPU.

- ti,rproc:		phandle to the wkup_m3 rproc node so the IPC driver

			can boot it.

- mboxes:		phandles used by IPC framework to get correct mbox

			channel for communication. Must point to appropriate

			mbox_wkupm3 child node.

Example:

--------

/* AM33xx */

	l4_wkup: l4_wkup@44c00000 {

		...

		scm: scm@210000 {

			compatible = "ti,am3-scm", "simple-bus";

			reg = <0x210000 0x2000>;

			#address-cells = <1>;

			#size-cells = <1>;

			ranges = <0 0x210000 0x2000>;

			...

			wkup_m3_ipc: wkup_m3_ipc@1324 {

				compatible = "ti,am3352-wkup-m3-ipc";

				reg = <0x1324 0x24>;

				interrupts = <78>;

				ti,rproc = <&wkup_m3>;

				mboxes = <&mailbox &mbox_wkupm3>;

			};

			...

		};

	};