NVIDIA Tegra 20 AC97 controller

Required properties:
- compatible : "nvidia,tegra20-ac97"
- reg : Should contain AC97 controller registers location and length
- interrupts : Should contain AC97 interrupt
- nvidia,dma-request-selector : The Tegra DMA controller's phandle and
  request selector for the AC97 controller
- nvidia,codec-reset-gpio : The Tegra GPIO controller's phandle and the number
  of the GPIO used to reset the external AC97 codec
- nvidia,codec-sync-gpio : The Tegra GPIO controller's phandle and the number
  of the GPIO corresponding with the AC97 DAP _FS line
Example:

ac97@70002000 {
	compatible = "nvidia,tegra20-ac97";
	reg = <0x70002000 0x200>;
	interrupts = <0 81 0x04>;
	nvidia,dma-request-selector = <&apbdma 12>;
	nvidia,codec-reset-gpio = <&gpio 170 0>;
	nvidia,codec-sync-gpio = <&gpio 120 0>;
};
