ASoC: qi_lb60: Use GPIO descriptor API

The new GPIO descriptor API is now the preferred way for handling GPIOs. It also
allows us to separate the platform depended code from the platform independent
code (Which will make it possible to increase build test coverage of the
platform independent code).

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Mark Brown <broonie@linaro.org>