UniPhier UART controller

Required properties:
- compatible: should be "socionext,uniphier-uart".
- reg: offset and length of the register set for the device.
- interrupts: a single interrupt specifier.
- clocks: phandle to the input clock.

Optional properties:
- fifo-size: the RX/TX FIFO size.  Defaults to 64 if not specified.

Example:
	aliases {
		serial0 = &serial0;
	};

	serial0: serial@54006800 {
		compatible = "socionext,uniphier-uart";
		reg = <0x54006800 0x40>;
		interrupts = <0 33 4>;
		clocks = <&uart_clk>;
		fifo-size = <64>;
	};