tegra: sound: Add an I2S driver

Add a driver which supports transmitting digital sound to an audio codec.
This uses fixed parameters as a device-tree binding is not currently
defined.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>