ASoC: Intel: Skylake: fix Kconfigs, make HDaudio codec optional

The Skylake driver currently has a set of problems supporting
load/unload modules. We need to make the HDaudio codec support
optional to help narrow down the issues.

Support for HDaudio codecs also leads to a Kconfig issue. We want the
hdac_hda codec to be compilable independently of Skylake (e.g. with
ALL_CODECS) but when Skylake is selected as built-in the hdac_hda
codec needs to use the same option due a a code dependency

Solve both problems by adding a user-selectable boolean Kconfig,
select HDAC_HDA as needed and make the HDaudio codec support in the
Skylake driver optional. Tests on a Chell Chromebook device without
HDaudio show no regression for speaker and HDMI playback.

This is submitted as an RFC to allow for comments and more validation.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>