Add Soundwire Slave driver for the WCD9390/WCD9395 Audio Codec.

The WCD9390/WCD9395 Soundwire devices will be used by the
main WCD9390/WCD9395 Audio Codec driver to access registers
and configure Soundwire RX and TX ports.
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://msgid.link/r/20231219-topic-sm8650-upstream-wcd939x-codec-v4-4-1c3bbff2d7ab@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>