ASoC: tegra: add tegra30-ahub driver

The AHUB (Audio Hub) is a mux/crossbar which links all audio-related
devices except the HDA controller on Tegra30. The devices include the
DMA FIFOs, DAM (Digital Audio Mixers), I2S controllers, and SPDIF
controller. Audio data may be routed between these devices in various
combinations as required by board design/application.

Includes a squashed bugfix from Nikesh Oswal <noswal@nvidia.com>
Includes squashed bugfixes from Sumit Bhattacharya <sumitb@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

Documentation/devicetree/bindings/sound/nvidia,tegra30-ahub.txt

+NVIDIA Tegra30 AHUB (Audio Hub)
+
+Required properties:
+- compatible : "nvidia,tegra30-ahub"
+- reg : Should contain the register physical address and length for each of
+  the AHUB's APBIF registers and the AHUB's own registers.
+- interrupts : Should contain AHUB interrupt
+- nvidia,dma-request-selector : The Tegra DMA controller's phandle and
+  request selector for the first APBIF channel.
+- ranges : The bus address mapping for the configlink register bus.
+  Can be empty since the mapping is 1:1.
+- #address-cells : For the configlink bus. Should be <1>;
+- #size-cells : For the configlink bus. Should be <1>.
+
+AHUB client modules need to specify the IDs of their CIFs (Client InterFaces).
+For RX CIFs, the numbers indicate the register number within AHUB routing
+register space (APBIF 0..3 RX, I2S 0..5 RX, DAM 0..2 RX 0..1, SPDIF RX 0..1).
+For TX CIFs, the numbers indicate the bit position within the AHUB routing
+registers (APBIF 0..3 TX, I2S 0..5 TX, DAM 0..2 TX, SPDIF TX 0..1).
+
+Example:
+
+ahub@70080000 {
+	compatible = "nvidia,tegra30-ahub";
+	reg = <0x70080000 0x200 0x70080200 0x100>;
+	interrupts = < 0 103 0x04 >;
+	nvidia,dma-request-selector = <&apbdma 1>;
+
+	ranges;
+	#address-cells = <1>;
+	#size-cells = <1>;
+};