arm: mach-mvebu: add documentation for new device tree bindings

Marvell Armada 370 and Armada XP Interrupt Controller

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

Required properties:

- compatible: Should be "marvell,mpic"

- interrupt-controller: Identifies the node as an interrupt controller.

- #interrupt-cells: The number of cells to define the interrupts. Should be 1.

  The cell is the IRQ number

- reg: Should contain PMIC registers location and length. First pair

  for the main interrupt registers, second pair for the per-CPU

  interrupt registers

Example:

        mpic: interrupt-controller@d0020000 {

              compatible = "marvell,mpic";

              #interrupt-cells = <1>;

              #address-cells = <1>;

              #size-cells = <1>;

              interrupt-controller;

              reg = <0xd0020000 0x1000>,

                    <0xd0021000 0x1000>;

        };

Marvell Armada 370 and Armada XP Global Timers

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

Required properties:

- compatible: Should be "marvell,armada-370-xp-timer"

- interrupts: Should contain the list of Global Timer interrupts

- reg: Should contain the base address of the Global Timer registers

Optional properties:

- marvell,timer-25Mhz: Tells whether the Global timer supports the 25

  Mhz fixed mode (available on Armada XP and not on Armada 370)

Marvell Armada 370 and Armada XP Platforms Device Tree Bindings

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

Boards with a SoC of the Marvell Armada 370 and Armada XP families

shall have the following property:

Required root node property:

compatible: must contain "marvell,armada-370-xp"

In addition, boards using the Marvell Armada 370 SoC shall have the

following property:

Required root node property:

compatible: must contain "marvell,armada370"

In addition, boards using the Marvell Armada XP SoC shall have the

following property:

Required root node property:

compatible: must contain "marvell,armadaxp"

MVEBU System Controller

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

MVEBU (Marvell SOCs: Armada 370/XP, Dove, mv78xx0, Kirkwood, Orion5x)

Required properties:

- compatible: one of:

	- "marvell,orion-system-controller"

	- "marvell,armada-370-xp-system-controller"

- reg: Should contain system controller registers location and length.

Example:

	system-controller@d0018200 {

		compatible = "marvell,armada-370-xp-system-controller";

		reg = <0xd0018200 0x500>;

	};