ASoC: tegra: Remove SoC-specific Kconfig depends and selects

This removes the SoC-specific dependencies on the platform drivers,
as well as SoC-specific selections of platform drivers for the
machine drivers. The rationale behind this change is that the
dependencies are not actual build dependencies but run-time ones.

The previously listed SoCs were also incomplete: for instance, tegra124
uses the tegra30 platform drivers, which could not be built without
ARCH_TEGRA_3x_SOC set.

Descriptions of the tristates are also added to allow these options
to be set via defconfig/menuconfig.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>