Documentation: devicetree: add epson rx6110 binding

Epson RX6110 Real Time Clock

============================

The Epson RX6110 can be used with SPI or I2C busses. The kind of

bus depends on the SPISEL pin and can not be configured via software.

I2C mode

--------

Required properties:

  - compatible: should be: "epson,rx6110"

  - reg : the I2C address of the device for I2C

Example:

	rtc: rtc@32 {

		compatible = "epson,rx6110"

		reg = <0x32>;

	};

SPI mode

--------

Required properties:

  - compatible: should be: "epson,rx6110"

  - reg: chip select number

  - spi-cs-high: RX6110 needs chipselect high

  - spi-cpha: RX6110 works with SPI shifted clock phase

  - spi-cpol: RX6110 works with SPI inverse clock polarity

Example:

	rtc: rtc@3 {

		compatible = "epson,rx6110"

		reg = <3>

		spi-cs-high;

		spi-cpha;

		spi-cpol;

	};