ARM: tegra: Add Tegra I2S interfaces to defconfig

This selects both the Tegra20 and Tegra30 I2S interfaces (that were
previously auto-selected by Kconfig but are not anymore) to
tegra_defconfig, as built-ins.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Thierry Reding <treding@nvidia.com>