ASoC: sunxi: Add Allwinner A10 Digital Audio driver

The Allwinner A10 and later come with a hardware block that used for the
PCM and I2S interfaces.

Add a driver for it in ASoC.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Tested-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>