ALSA: control: Optimize locking for look-up

For a fast look-up of a control element via either numid or name
matching (enabled via CONFIG_SND_CTL_FAST_LOOKUP), a locking isn't
needed at all thanks to Xarray.  OTOH, the locking is still needed for
a slow linked-list traversal, and that's rather a rare case.

In this patch, we reduce the use of locking at snd_ctl_find_*() API
functions, and switch from controls_rwsem to controls_rwlock for
avoiding unnecessary lock inversions.  This also resulted in a nice
cleanup, as *_unlocked() version of snd_ctl_find_*() APIs can be
dropped.

snd_ctl_find_id_mixer_unlocked() is still left just as an alias of
snd_ctl_find_id_mixer(), since soc-card.c has a wrapper and there are
several users.  Once after converting there, we can remove it later.

Signed-off-by: Takashi Iwai <[email protected]>
Link: https://patch.msgid.link/[email protected]

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