NVIDIA Tegra20/Tegra30 high speed (DMA based) UART controller driver.

Required properties:
- compatible : should be "nvidia,tegra30-hsuart", "nvidia,tegra20-hsuart".
- reg: Should contain UART controller registers location and length.
- interrupts: Should contain UART controller interrupts.
- clocks: Must contain one entry, for the module clock.
  See ../clocks/clock-bindings.txt for details.
- resets : Must contain an entry for each entry in reset-names.
  See ../reset/reset.txt for details.
- reset-names : Must include the following entries:
  - serial
- dmas : Must contain an entry for each entry in dma-names.
  See ../dma/dma.txt for details.
- dma-names : Must include the following entries:
  - rx
  - tx

Optional properties:
- nvidia,enable-modem-interrupt: Enable modem interrupts. Should be enable
		only if all 8 lines of UART controller are pinmuxed.

Example:

serial@70006000 {
	compatible = "nvidia,tegra30-hsuart", "nvidia,tegra20-hsuart";
	reg = <0x70006000 0x40>;
	reg-shift = <2>;
	interrupts = <0 36 0x04>;
	nvidia,enable-modem-interrupt;
	clocks = <&tegra_car 6>;
	resets = <&tegra_car 6>;
	reset-names = "serial";
	dmas = <&apbdma 8>, <&apbdma 8>;
	dma-names = "rx", "tx";
};