ASoC: Intel: Skylake: Combine snd_soc_skl_ipc and snd_soc_skl

ASoC: Intel: Skylake: Combine snd_soc_skl_ipc and snd_soc_skl

As both modules are core part of Skylake driver and none can live
without the other, combine snd_soc_skl_ipc and snd_soc_skl.

It's highly probable IPC module was to be treated as an interface for
platform specific code implementations e.g.: possibility of existence of
BXT specific code without SKL one. However, most funtionalities are
being inherited from one DSP firmware to another, and thus this
assumption fails.

skl-sst, bxt-sst and cnl-sst are not individuals pointing respectively
to SKL (cAVS 1.5), BXT (cAVS 1.5+) & CNL (cAVS 1.8) standalone
implementations. Code found within these is shared among all platforms
whenever necessary to avoid code duplication and reduce development
burden.

Merge also helps in cleaning up internal code in future changes.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@intel.com>
Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20190723145854.8527-3-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>