* Synopsys DesignWare ABP UART

Required properties:
- compatible : "snps,dw-apb-uart"
- reg : offset and length of the register set for the device.
- interrupts : should contain uart interrupt.

Clock handling:
The clock rate of the input clock needs to be supplied by one of
- clock-frequency : the input clock frequency for the UART.
- clocks : phandle to the input clock

The supplying peripheral clock can also be handled, needing a second property
- clock-names: tuple listing input clock names.
	Required elements: "baudclk", "apb_pclk"

Optional properties:
- snps,uart-16550-compatible : reflects the value of UART_16550_COMPATIBLE
  configuration parameter. Define this if your UART does not implement the busy
  functionality.
- resets : phandle to the parent reset controller.
- reg-shift : quantity to shift the register offsets by.  If this property is
  not present then the register offsets are not shifted.
- reg-io-width : the size (in bytes) of the IO accesses that should be
  performed on the device.  If this property is not present then single byte
  accesses are used.
- dcd-override : Override the DCD modem status signal. This signal will always
  be reported as active instead of being obtained from the modem status
  register. Define this if your serial port does not use this pin.
- dsr-override : Override the DTS modem status signal. This signal will always
  be reported as active instead of being obtained from the modem status
  register. Define this if your serial port does not use this pin.
- cts-override : Override the CTS modem status signal. This signal will always
  be reported as active instead of being obtained from the modem status
  register. Define this if your serial port does not use this pin.
- ri-override : Override the RI modem status signal. This signal will always be
  reported as inactive instead of being obtained from the modem status register.
  Define this if your serial port does not use this pin.

Example:

	uart@80230000 {
		compatible = "snps,dw-apb-uart";
		reg = <0x80230000 0x100>;
		clock-frequency = <3686400>;
		interrupts = <10>;
		reg-shift = <2>;
		reg-io-width = <4>;
		dcd-override;
		dsr-override;
		cts-override;
		ri-override;
	};

Example with one clock:

	uart@80230000 {
		compatible = "snps,dw-apb-uart";
		reg = <0x80230000 0x100>;
		clocks = <&baudclk>;
		interrupts = <10>;
		reg-shift = <2>;
		reg-io-width = <4>;
	};

Example with two clocks:

	uart@80230000 {
		compatible = "snps,dw-apb-uart";
		reg = <0x80230000 0x100>;
		clocks = <&baudclk>, <&apb_pclk>;
		clock-names = "baudclk", "apb_pclk";
		interrupts = <10>;
		reg-shift = <2>;
		reg-io-width = <4>;
	};
