serial/imx: add device tree probe support

It adds device tree probe support for imx tty/serial driver.

Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>
Signed-off-by: Jason Liu <jason.hui@linaro.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Grant Likely <grant.likely@secretlab.ca>

Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt

@@ -0,0 +1,19 @@
+* 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
+
+Example:
+
+uart@73fbc000 {
+	compatible = "fsl,imx51-uart", "fsl,imx21-uart";
+	reg = <0x73fbc000 0x4000>;
+	interrupts = <31>;
+	fsl,uart-has-rtscts;
+};