Add a hook to struct hda_codec for filtering the target power state of
each widget when powering up/down.  The current hackish EAPD check is
implemented as the default hook pointer, too.

This allows codec drivers to implement own power filter.  In the
upcoming changes, the generic parser will have the better power filter
based on the active paths.

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