ASoC: wm8940: add devicetree support

This adds devicetree support to the wm8940 codec driver.
With a DT-based kernel, there is no board-specific setting
to select the driver so allow it to be manually chosen.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20220509121055.31103-1-lukma@denx.de


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