The amp hash table was used for recording the cached reads of some
capability values like pin caps or amp caps.  Now all these are moved
to regmap as well.

One addition to the regmap helper is codec->caps_overwriting flag.
This is set in snd_hdac_override_parm(), and the regmap helper accepts
any register while this flag is set, so that it can overwrite even the
read-only verb like AC_VERB_PARAMETERS.  The flag is cleared
immediately in snd_hdac_override_parm(), as it's a once-off flag.

Along with these changes, the no longer needed amp hash and relevant
fields are removed from hda_codec struct now.
Signed-off-by: Takashi Iwai <tiwai@suse.de>