Add an optional mic detect gpio property.  If specified in device tree
there will be a mic jack created for the given gpio.  This will be
used by the Tegra-based Chromebooks.
Signed-off-by: Dylan Reid <dgreid@chromium.org>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>