ALSA: core: Expose sound card online/offline state

Expose sound card online/offline state to procfs so userspace application
can poll and read sound card's state.

Change-Id: Ie605ad57f4ce5abf62a216e790407029658ac3c9
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>
Signed-off-by: Meng Wang <mwang@codeaurora.org>