ASoC: sun4i-i2s: Support more channels

We've been limited to 2 channels in the driver while the controller
supports from 1 to 8 channels, in both capture and playback. let's remove
the hardcoded checks and numbers, and extend the range of channel numbers
we can use.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://lore.kernel.org/r/27d9de5cd56f3a544851b8cd8af08bf836d19637.1566242458.git-series.maxime.ripard@bootlin.com


Signed-off-by: Mark Brown <broonie@kernel.org>