ASoC: Samsung: Add arndale_rt5631 machine driver and binding

Adding machine driver to instantiate I2S based realtek's ALC5631
sound card on Arndale board.

There are other variants of Audio Daughter Cards for Arndale
Board for which support already exists but there is no support for
Realtek's alc5631 codec hence support for ALC5631 based machine
driver is being added.
This patch also documents the device tree binding for the Arndale
board based machine driver.

Signed-off-by: Claude Youn <claude.youn@gmail.com>
Signed-off-by: Krishna Mohan Dani <krishna.md@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>