* Spreadtrum serial UART

Required properties:
- compatible: must be one of:
  * "sprd,sc9836-uart"
  * "sprd,sc9860-uart", "sprd,sc9836-uart"

- reg: offset and length of the register set for the device
- interrupts: exactly one interrupt specifier
- clock-names: Should contain following entries:
  "enable" for UART module enable clock,
  "uart" for UART clock,
  "source" for UART source (parent) clock.
- clocks: Should contain a clock specifier for each entry in clock-names.
  UART clock and source clock are optional properties, but enable clock
  is required.

Optional properties:
- dma-names: Should contain "rx" for receive and "tx" for transmit channels.
- dmas: A list of dma specifiers, one for each entry in dma-names.

Example:
	uart0: serial@0 {
		compatible = "sprd,sc9860-uart",
			     "sprd,sc9836-uart";
		reg = <0x0 0x100>;
		interrupts = <GIC_SPI 2 IRQ_TYPE_LEVEL_HIGH>;
		dma-names = "rx", "tx";
		dmas = <&ap_dma 19>, <&ap_dma 20>;
		clock-names = "enable", "uart", "source";
		clocks = <&clk_ap_apb_gates 9>, <&clk_uart0>, <&ext_26m>;
	};