soc: qcom: bgcom: protect rsb events list for producer/consumer

Provides lock to protect rsb event list for producer/
consumer. A node can be added or removed at a time to avoid
list corruption.

Change-Id: Ib91e5339e0b9e1f60d595bf9ef4d83a57f867f90
Signed-off-by: Arjun Singh <arsingh@codeaurora.org>