* ARMv7M System Timer

ARMv7-M includes a system timer, known as SysTick. Current driver only
implements the clocksource feature.

Required properties:
- compatible	  : Should be "arm,armv7m-systick"
- reg		  : The address range of the timer

Required clocking property, have to be one of:
- clocks	  : The input clock of the timer
- clock-frequency : The rate in HZ in input of the ARM SysTick

Examples:

systick: timer@e000e010 {
	compatible = "arm,armv7m-systick";
	reg = <0xe000e010 0x10>;
	clocks = <&clk_systick>;
};

systick: timer@e000e010 {
	compatible = "arm,armv7m-systick";
	reg = <0xe000e010 0x10>;
	clock-frequency = <90000000>;
};

Document the ARM System timer bindings
dt-bindings: Document the ARM System timer bindings

This adds documentation of device tree bindings for the
ARM System timer.

Tested-by: Chanwoo Choi <42eed19c0f56a8d487deac90c6d19d6364b7ba73@samsung.com>
Acked-by: Rob Herring <fbb37eacae100e13076d5c4b46f06cfa4d6fa9f8@kernel.org>
Signed-off-by: Maxime Coquelin <abf7af79b25008a2c9c1572d66f685a2834dde02@gmail.com>
Signed-off-by: Daniel Lezcano <e9fa45941f2ebe89c1b9d6c5f339ab42eadb8567@linaro.org>
