ASoC: io: Remove SPI support

All ASoC CODEC drivers that use SPI have now been converted to use regmap
so we can delete SND_SOC_SPI, preventing any new users being added.

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

diff --cc include/sound/soc.h
Simple merge

diff --cc sound/soc/soc-io.c
Simple merge