Lantiq SoC ASC serial controller

Required properties:
- compatible : Should be "lantiq,asc"
- reg : Address and length of the register set for the device
- interrupts: the 3 (tx rx err) interrupt numbers. The interrupt specifier
  depends on the interrupt-parent interrupt controller.

Example:

asc1: serial@e100c00 {
	compatible = "lantiq,asc";
	reg = <0xE100C00 0x400>;
	interrupt-parent = <&icu0>;
	interrupts = <112 113 114>;
};