ASoC: bg: Add support to handle ssr events in BG

Need to close all the active audio sessions when
modem or BG was down. Add support to handle subsytem
restart events from modem and BG.

Change-Id: Id1b3ae5ef6eac0bc3bfe9239cb411e0b91ae2153
Signed-off-by: Bala Kishore Pati <balakishorepati@codeaurora.org>