rtc: x1205: Add DT bindings

This adds device tree bindings for the Xircom X1205 RTC found
in the Linksys NSLU2.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
[alexandre.belloni@bootlin.com: move doc to rtc.txt]
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/rtc.txt

@@ -69,3 +69,4 @@ ricoh,rv5c386		I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
 ricoh,rv5c387a		I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
 sii,s35390a		2-wire CMOS real-time clock
 whwave,sd3078		I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
+xircom,x1205		Xircom X1205 I2C RTC