OMAP SSI controller bindings

OMAP3's Synchronous Serial Interface (SSI) controller implements a
legacy variant of MIPI's High Speed Synchronous Serial Interface (HSI),
while the controller found inside OMAP4 is supposed to be fully compliant
with the HSI standard.

Required properties:
- compatible:		Should include "ti,omap3-ssi" or "ti,omap4-hsi"
- reg-names:		Contains the values "sys" and "gdd" (in this order).
- reg:			Contains a matching register specifier for each entry
			in reg-names.
- interrupt-names:	Contains the value "gdd_mpu".
- interrupts: 		Contains matching interrupt information for each entry
			in interrupt-names.
- ranges:		Represents the bus address mapping between the main
			controller node and the child nodes below.
- clock-names:		Must include the following entries:
  "ssi_ssr_fck": The OMAP clock of that name
  "ssi_sst_fck": The OMAP clock of that name
  "ssi_ick": The OMAP clock of that name
- clocks:		Contains a matching clock specifier for each entry in
			clock-names.
- #address-cells:	Should be set to <1>
- #size-cells:		Should be set to <1>

Each port is represented as a sub-node of the ti,omap3-ssi device.

Required Port sub-node properties:
- compatible:		Should be set to the following value
			ti,omap3-ssi-port (applicable to OMAP34xx devices)
			ti,omap4-hsi-port (applicable to OMAP44xx devices)
- reg-names:		Contains the values "tx" and "rx" (in this order).
- reg:			Contains a matching register specifier for each entry
			in reg-names.
- interrupt-parent	Should be a phandle for the interrupt controller
- interrupts:		Should contain interrupt specifiers for mpu interrupts
			0 and 1 (in this order).
- ti,ssi-cawake-gpio:	Defines which GPIO pin is used to signify CAWAKE
			events for the port. This is an optional board-specific
			property. If it's missing the port will not be
			enabled.

Optional properties:
- ti,hwmods:		Shall contain TI interconnect module name if needed
			by the SoC

Example for Nokia N900:

ssi-controller@48058000 {
	compatible = "ti,omap3-ssi";

	/* needed until hwmod is updated to use the compatible string */
	ti,hwmods = "ssi";

	reg = <0x48058000 0x1000>,
	      <0x48059000 0x1000>;
	reg-names = "sys",
		    "gdd";

	interrupts = <55>;
	interrupt-names = "gdd_mpu";

	clocks = <&ssi_ssr_fck>,
		 <&ssi_sst_fck>,
		 <&ssi_ick>;
	clock-names = "ssi_ssr_fck",
		      "ssi_sst_fck",
		      "ssi_ick";

	#address-cells = <1>;
	#size-cells = <1>;
	ranges;

	ssi-port@4805a000 {
		compatible = "ti,omap3-ssi-port";

		reg = <0x4805a000 0x800>,
		      <0x4805a800 0x800>;
		reg-names = "tx",
			    "rx";

		interrupt-parent = <&intc>;
		interrupts = <67>,
			     <68>;

		ti,ssi-cawake-gpio = <&gpio5 23 GPIO_ACTIVE_HIGH>; /* 151 */
	}

	ssi-port@4805a000 {
		compatible = "ti,omap3-ssi-port";

		reg = <0x4805b000 0x800>,
		      <0x4805b800 0x800>;
		reg-names = "tx",
			    "rx";

		interrupt-parent = <&intc>;
		interrupts = <69>,
			     <70>;

	}
}