ASoC: sun4i-i2s: Add regmap fields for channels

On the original i2s block the channel mapping and selection were
configured for stereo audio by default: This is not the case with
the newer SoCs and they are also located at different offsets.

To support the newer SoC then regmap fields have been added to the
quirks and these are initialised to their correct settings during
probing.

Signed-off-by: Marcus Cooper <codekipper@gmail.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>