ASoC: Tegra: Harmony: Don't use soc-audio platform device

Previously, snd-soc-tegra-harmony internally instantiated a platform device
object whenever the module was loaded. Instead, switch to a more typical model
where arch/arm/mach-tegra defines a platform device, and snd-soc-tegra-harmony
acts as a driver for such a platform device.

Define a new struct tegra_harmony to store driver data in the future.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>