ASoC: wcd_cpe_services: Fix possible race conditions

It is possible that cpe service API's can be invoked from multiple
thread contexts which can result into race conditions while
accesing/updating the lists and other internal state variables. Some of
these race conditions can cause device crash. Fix the race conditions by
protecting the internal lists/state variables with mutex.

CRs-fixed: 735730
Change-Id: I937efd1cf4f7af6a6a760f022edf8ecc081e63d6
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>