dt-bindings: timer: Add Milbeaut M10V timer description

Milbeaut SoCs Timer Controller

Required properties:

- compatible : should be "socionext,milbeaut-timer".

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

- interrupts : The interrupt of the first timer.

- clocks: phandle to the input clk.

Example:

timer {

	compatible = "socionext,milbeaut-timer";

	reg = <0x1e000050 0x20>

	interrupts = <0 91 4>;

	clocks = <&clk 4>;

};