ASoC: atmel: add wm8904 based audio machine driver

Add wm8904 based audio machine driver for Atmel EK board

The following ek board based on it
  - at91sam9n12ek
  - sama5d3xek (d31, d33, d34, d35)

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>