ASoC: tegra: Remove TEGRA_I2S_AUDIO from Kconfig

That config variable doesn't exist in the mainline kernel, and hence
the dependency shouldn't either.

In linux-tegra-2.6.36, the dependency did exist to avoid a conflict with
the old non-ALSA Tegra I2S driver. However, this isn't and won't be
upstreamed.

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>