ASoC: tegra: support a Mic Jack in the Tegra+RT5640 machine driver

Add a Mic Jack widget to the Tegra+RT5640 machine driver, and document
this in the DT binding. This enables the DT to include the Mic Jack in
the audio routing table, and hence enables capture of audio, in addition
to the previously-working playback.

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