ASoC: Tegra+WM8903 machine: Add device tree binding

This driver is parameterized in two ways:

a) Platform data, which supplies the set of GPIOs used by the driver.
   These GPIOs can now be parsed out of device tree.

b) Machine-specific DAPM route arrays embedded into the ASoC machine
   driver itself. Historically, the driver picks the appropriate array
   to use using machine_is_*(). The driver now requires this array to
   be parsed from device tree when instantiated through device tree,
   using the core ASoC support for this parsing.

Based on work by John Bonesio, but significantly reworked since then.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>