bindings: Add dt-bindings for arch_timer

* ARM architected timer

ARM cores may have a per-core architected timer, which provides per-cpu timers,

or a memory mapped architected timer, which provides up to 8 frames with a

physical and optional virtual timer per frame.

The per-core architected timer is attached to a GIC to deliver its

per-processor interrupts via PPIs. The memory mapped timer is attached to a GIC

to deliver its interrupts via SPIs.

** CP15 Timer node properties:

- compatible : Should at least contain one of

	"arm,armv7-timer"

	"arm,armv8-timer"

- interrupts : Interrupt list for secure, non-secure, virtual and

  hypervisor timers, in that order.

- clock-frequency : The frequency of the main counter, in Hz. Should be present

  only where necessary to work around broken firmware which does not configure

  CNTFRQ on all CPUs to a uniform correct value. Use of this property is

  strongly discouraged; fix your firmware unless absolutely impossible.

- always-on : a boolean property. If present, the timer is powered through an

  always-on power domain, therefore it never loses context.

- fsl,erratum-a008585 : A boolean property. Indicates the presence of

  QorIQ erratum A-008585, which says that reading the counter is

  unreliable unless the same value is returned by back-to-back reads.

  This also affects writes to the tval register, due to the implicit

  counter read.

- hisilicon,erratum-161010101 : A boolean property. Indicates the

  presence of Hisilicon erratum 161010101, which says that reading the

  counters is unreliable in some cases, and reads may return a value 32

  beyond the correct value. This also affects writes to the tval

  registers, due to the implicit counter read.

** Optional properties:

- arm,cpu-registers-not-fw-configured : Firmware does not initialize

  any of the generic timer CPU registers, which contain their

  architecturally-defined reset values. Only supported for 32-bit

  systems which follow the ARMv7 architected reset values.

- arm,no-tick-in-suspend : The main counter does not tick when the system is in

  low-power system suspend on some SoCs. This behavior does not match the

  Architecture Reference Manual's specification that the system counter "must

  be implemented in an always-on power domain."

Example:

	timer {

		compatible = "arm,cortex-a15-timer",

			     "arm,armv7-timer";

		interrupts = <1 13 0xf08>,

			     <1 14 0xf08>,

			     <1 11 0xf08>,

			     <1 10 0xf08>;

		clock-frequency = <100000000>;

	};

** Memory mapped timer node properties:

- compatible : Should at least contain "arm,armv7-timer-mem".

- clock-frequency : The frequency of the main counter, in Hz. Should be present

  only when firmware has not configured the MMIO CNTFRQ registers.

- reg : The control frame base address.

Note that #address-cells, #size-cells, and ranges shall be present to ensure

the CPU can address a frame's registers.

A timer node has up to 8 frame sub-nodes, each with the following properties:

- frame-number: 0 to 7.

- interrupts : Interrupt list for physical and virtual timers in that order.

  The virtual timer interrupt is optional.

- reg : The first and second view base addresses in that order. The second view

  base address is optional.

- status : "disabled" indicates the frame is not available for use. Optional.

Example:

	timer@f0000000 {

		compatible = "arm,armv7-timer-mem";

		#address-cells = <1>;

		#size-cells = <1>;

		ranges;

		reg = <0xf0000000 0x1000>;

		clock-frequency = <50000000>;

		frame@f0001000 {

			frame-number = <0>

			interrupts = <0 13 0x8>,

				     <0 14 0x8>;

			reg = <0xf0001000 0x1000>,

			      <0xf0002000 0x1000>;

		};

		frame@f0003000 {

			frame-number = <1>

			interrupts = <0 15 0x8>;

			reg = <0xf0003000 0x1000>;

		};

	};