devtree: add binding documentation for sp804

ARM sp804 Dual Timers

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Required properties:

- compatible: Should be "arm,sp804" & "arm,primecell"

- interrupts: Should contain the list of Dual Timer interrupts. This is the

	interrupt for timer 1 and timer 2. In the case of a single entry, it is

	the combined interrupt or if "arm,sp804-has-irq" is present that

	specifies which timer interrupt is connected.

- reg: Should contain location and length for dual timer register.

- clocks: clocks driving the dual timer hardware. This list should be 1 or 3

	clocks.	With 3 clocks, the order is timer0 clock, timer1 clock,

	apb_pclk. A single clock can also be specified if the same clock is

	used for all clock inputs.

Optional properties:

- arm,sp804-has-irq = <#>: In the case of only 1 timer irq line connected, this

	specifies if the irq connection is for timer 1 or timer 2. A value of 1

	or 2 should be used.

Example:

	timer0: timer@fc800000 {

		compatible = "arm,sp804", "arm,primecell";

		reg = <0xfc800000 0x1000>;

		interrupts = <0 0 4>, <0 1 4>;

		clocks = <&timclk1 &timclk2 &pclk>;

		clock-names = "timer1", "timer2", "apb_pclk";

	};