ASoC: codecs: adau1701: add DT bindings

Apart from pure matching, the bindings also support setting the the
reset gpio line.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>