* Atmel SSC driver.

Required properties:
- compatible: "atmel,at91rm9200-ssc" or "atmel,at91sam9g45-ssc"
	- atmel,at91rm9200-ssc: support pdc transfer
	- atmel,at91sam9g45-ssc: support dma transfer
- reg: Should contain SSC registers location and length
- interrupts: Should contain SSC interrupt
- clock-names: tuple listing input clock names.
	Required elements: "pclk"
- clocks: phandles to input clocks.


Required properties for devices compatible with "atmel,at91sam9g45-ssc":
- dmas: DMA specifier, consisting of a phandle to DMA controller node,
  the memory interface and SSC DMA channel ID (for tx and rx).
  See Documentation/devicetree/bindings/dma/atmel-dma.txt for details.
- dma-names: Must be "tx", "rx".

Optional properties:
  - atmel,clk-from-rk-pin: bool property.
     - When SSC works in slave mode, according to the hardware design, the
       clock can get from TK pin, and also can get from RK pin. So, add
       this parameter to choose where the clock from.
     - By default the clock is from TK pin, if the clock from RK pin, this
       property is needed.

Examples:
- PDC transfer:
ssc0: ssc@fffbc000 {
	compatible = "atmel,at91rm9200-ssc";
	reg = <0xfffbc000 0x4000>;
	interrupts = <14 4 5>;
	clocks = <&ssc0_clk>;
	clock-names = "pclk";
};

- DMA transfer:
ssc0: ssc@f0010000 {
      compatible = "atmel,at91sam9g45-ssc";
      reg = <0xf0010000 0x4000>;
      interrupts = <28 4 5>;
      dmas = <&dma0 1 13>,
	     <&dma0 1 14>;
      dma-names = "tx", "rx";
      pinctrl-names = "default";
      pinctrl-0 = <&pinctrl_ssc0_tx &pinctrl_ssc0_rx>;
      status = "disabled";
};