BACKPORT: ALSA: timer: Handle disconnection more safely

[ Upstream commit 230323dac060123c340cf75997971145a42661ee ]

Currently ALSA timer device doesn't take the disconnection into
account very well; it merely unlinks the timer device at disconnection
callback but does nothing else.  Because of this, when an application
accessing the timer device is disconnected, it may release the
resource before actually closed.  In most cases, it results in a
warning message indicating a leftover timer instance like:
   ALSA: timer xxxx is busy?
But basically this is an open race.

This patch tries to address it.  The strategy is like other ALSA
devices: namely,
- Manage card's refcount at each open/close
- Wake up the pending tasks at disconnection
- Check the shutdown flag appropriately at each possible call

Note that this patch has one ugly hack to handle the wakeup of pending
tasks.  It'd be cleaner to introduce a new disconnect op to
snd_timer_instance ops.  But since it would lead to internal ABI
breakage and it eventually increase my own work when backporting to
stable kernels, I took a different path to implement locally in
timer.c.  A cleanup patch will follow at next for 4.5 kernel.

Bug: 37240993
Change-Id: I05c7f0e7d28b63fc343091f800ceae9ec2afe4a4
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109431
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Siqi Lin <siqilin@google.com>
(cherry picked from commit 230323dac060123c340cf75997971145a42661ee)

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