Add support for the MikroElektronika PROTO audio codec board.

URL to the audio chip:
http://www.mikroe.com/add-on-boards/audio-voice/audio-codec-proto/Signed-off-by: NFlorian Meier <florian.meier@koalo.de>
Signed-off-by: NCodrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: NMark Brown <broonie@kernel.org>