* Atmel Universal Synchronous Asynchronous Receiver/Transmitter (USART)

Required properties:
- compatible: Should be "atmel,<chip>-usart"
  The compatible <chip> indicated will be the first SoC to support an
  additional mode or an USART new feature.
- reg: Should contain registers location and length
- interrupts: Should contain interrupt

Optional properties:
- atmel,use-dma-rx: use of PDC or DMA for receiving data
- atmel,use-dma-tx: use of PDC or DMA for transmitting data

<chip> compatible description:
- at91rm9200:  legacy USART support
- at91sam9260: generic USART implementation for SAM9 SoCs

Example:

	usart0: serial@fff8c000 {
		compatible = "atmel,at91sam9260-usart";
		reg = <0xfff8c000 0x4000>;
		interrupts = <7>;
		atmel,use-dma-rx;
		atmel,use-dma-tx;
	};