This patch adds the cache for codec command registers.
snd_hda_codec_write_cache() and snd_hda_sequence_write_cache() do
the write operations with caching, which values can be resumed via
snd_hda_codec_resume_cache().
The patch introduces only the framework, and no codec code is using
this cache yet.  It'll be implemented in the following patch.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>