ASoC: tegra: rename Tegra20-specific driver files

Rename these files so they include a specific hardware version in their
filenames. The contents is only touched minimally so that git's rename
tracking operates correctly; renaming all symbols in the files results
in a diff so large that the rename detection fails.

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