* Freescale i.MX Universal Asynchronous Receiver/Transmitter (UART)

Required properties:
- compatible : Should be "fsl,<soc>-uart"
- reg : Address and length of the register set for the device
- interrupts : Should contain uart interrupt

Optional properties:
- fsl,uart-has-rtscts : Indicate the uart has rts and cts
- fsl,irda-mode : Indicate the uart supports irda mode
- fsl,enable-dma :
	This enables (S)DMA for the uart. DMA is used for TX and RX. Note
	that for TX even for 1 byte to be transfered a DMA transfer is
	initiated. This can be changed by additionally use fsl,tx-auto-mode,
	see below.
- fsl,uart-dma-events : defines the DMA events (interrupts) for RX and TX.
	The first is the RX event, while the second is TX.
- fsl,enable-dte: Indicate the uart works in DTE mode
- fsl,uart-dma-rxbufsize : Configure RX DMA buffer size.
- fsl,tx-auto-mode: Indicate the TX part of uart works in AUTO mode.
	AUTO mode does mean that for
	* TX transfers: For TX transmissions <= fsl,tx-auto-mode-threshold
	  PIO mode (i.e. no DMA) is used. While for TX transfers
	  > fsl,tx-auto-mode-threshold a TX DMA transfer is initiated.
	  Together with the fsl,enable-dma above this can be used to
	  prevent TX DMA transfers for <= fsl,tx-auto-mode-threshold to
	  optimize the overhead needed to set up DMA transfers for small
	  data sizes.
	* RX transfers: If fsl,tx-auto-mode is set, only, RX is used in PIO
	  mode. If fsl,enable-dma and fsl,tx-auto-mode are set, RX is used
	  in DMA mode. I.e. fsl,enable-dma controls the RX mode if used
	  together with fsl,tx-auto-mode.
- fsl,tx-auto-mode-threshold: Configure Maximum data size transfer in PIO mode.
	This is used together with fsl,tx-auto-mode. If set, it defines the
	threshold to switch between TX PIO and TX DMA transfers. If not set,
	by default (fsl,tx-auto-mode is set, only), half of the uart FIFO
	size - 1 is taken as the threshold. E.g. with 32 bytes FIFO size in i.MX6
	this threshold is configured to 15 by default. Change this default by
	setting fsl,tx-auto-mode-threshold. Example:
	TX transfer size <= fsl,tx-auto-mode-threshold (default 15): TX PIO mode
	TX transfer size > fsl,tx-auto-mode-threshold (default 15): TX DMA mode

Example:

serial@73fbc000 {
	compatible = "fsl,imx51-uart", "fsl,imx21-uart";
	reg = <0x73fbc000 0x4000>;
	interrupts = <31>;
	fsl,uart-has-rtscts;
	fsl,enable-dma;
	fsl,uart-dma-events = <xx xx>;
	fsl,enable-dte;
	fsl,uart-dma-rxbufsize = <xx>;
	fsl,tx-auto-mode;
	fsl,tx-auto-mode-threshold = <xx>;
};
