ASoC: wm8731: Factor out the I2C and SPI bus code into separate modules

Placing both the I2C and SPI code in the same module causes problems with
mixes of modular and non-modular builds of the buses so it's generally bad
practice. As with other drivers split the bus code out of the WM8731 driver
into separate modules.

Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20220325153121.1598494-6-broonie@kernel.org


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