ASoC: tegra: tegra20_das: Fold header file into only user

ASoC: tegra: tegra20_das: Fold header file into only user

Since commit b4056cba65be ("ASoC: tegra: remove unnecessary includes")
the header file (which at the time was named tegra_das.h) there is only
the actual driver that includes it. Just move the definitions into the
driver, drop the exports and remove the completely unused function.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220629194224.175607-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>