ARM: dts: sun6i: Add audio codec device node

The A31 SoC includes the Allwinner audio codec, capable of 24-bit
playback up to 192 kHz and 24-bit capture up to 48 kHz.

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