IPC: add bus lock protect for ipc_device_list

IPC: add bus lock protect for ipc_device_list

BZ: 37748

In current IPC framework, ipc_device_list is not under protect by bus
lock, which may cause synchronization problem when they are accessed by
multi process at the same time. This patch puts it under protect of bus
lock to avoid this risk.

Change-Id: Ic48f2eb291ef900b1f1c498a3b6e7efb3fff8737
Signed-off-by: Shijie Zhang <shijie.zhang@intel.com>
Reviewed-on: http://android.intel.com:8080/49725
Reviewed-by: Yang, Bin <bin.yang@intel.com>
Reviewed-by: Chen, Jie D <jie.d.chen@intel.com>
Reviewed-by: Du, Alek <alek.du@intel.com>
Tested-by: Tang, HaifengX <haifengx.tang@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>