ALSA: hda - Add cache support for COEF read/write

The 16bit COEF read/write is pretty standard for many codecs, and they
can be cached in most cases -- more importantly, they need to be
restored at resume.  For making this easier, add the cache support to
regmap.  If the codec driver wants to cache the COEF access, set
codec->cache_coef flag and issue AC_VERB_GET_PROC_COEF with the coef
index in LSB 8 bits.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/hdaudio.h

@@ -78,6 +78,7 @@ struct hdac_device {
 	struct snd_array vendor_verbs;
 	bool lazy_cache:1;	/* don't wake up for writes */
 	bool caps_overwriting:1; /* caps overwrite being in process */
+	bool cache_coef:1;	/* cache COEF read/write too */
 };
 
 /* device/driver type used for matching */