* RS485 serial communications

The RTS signal is capable of automatically controlling line direction for
the built-in half-duplex mode.
The properties described hereafter shall be given to a half-duplex capable
UART node.

Required properties:
- rs485-rts-delay: prop-encoded-array <a b> where:
  * a is the delay between rts signal and beginning of data sent in milliseconds.
      it corresponds to the delay before sending data.
  * b is the delay between end of data sent and rts signal in milliseconds
      it corresponds to the delay after sending data and actual release of the line.

Optional properties:
- linux,rs485-enabled-at-boot-time: empty property telling to enable the rs485
  feature at boot time. It can be disabled later with proper ioctl.
- rs485-rx-during-tx: empty property that enables the receiving of data even
  whilst sending data.

RS485 example for Atmel USART:
	usart0: serial@fff8c000 {
		compatible = "atmel,at91sam9260-usart";
		reg = <0xfff8c000 0x4000>;
		interrupts = <7>;
		atmel,use-dma-rx;
		atmel,use-dma-tx;
		linux,rs485-enabled-at-boot-time;
		rs485-rts-delay = <0 200>;		// in milliseconds
	};