ASoC: Intel: sof_sdw: clean-up inclusion of header files

ASoC: Intel: sof_sdw: clean-up inclusion of header files

"struct snd_soc_dapm_widget" and "struct snd_kcontrol_new" are used in most
of these .c files. Adding the header files to prevent from depending on
<sound/soc.h>

Reported-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200821195603.215535-17-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>