ASoC: tegra: complete Tegra->Tegra20 renaming

Rename Tegra20-specific Kconfig variables, module filenames, all internal
symbol names, clocks, and platform devices, to reflect the fact the DAS
and I2S drivers are for a specific HW version.

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