ASoC: hdac_hda: add asoc extension for legacy HDA codec drivers

This patch adds a kernel module which is used by the legacy HDA
codec drivers as library. This implements hdac_ext_bus_ops to enable
the reuse of legacy HDA codec drivers with ASoC platform drivers.

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