ASoC: Add codec driver for AK5386

Adds a driver for Asahi Kasei's AK5386 Single-ended 24-Bit 192kHz
delta-sigma ADC. The device has no control port interface but an
optional RESET/PDN GPIO pin.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>