ASoC: Intel: fix interface for Chromebook machine drivers

The changes for HDaudio overlooked the fact that the machine drivers
used for Chromebooks rely on the dmic number information passed as
pdata.

Add dmic_num field to standard interface and use standard interface
instead of SKL-specific one.

Also clean-up pdata definition to remove fields that are no longer
used.

Fixes: 842bb513

 ('ASoC: Intel: use standard interface for Hdaudio machine driver')
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>