msm: ipc_logging: Replace spinlock_t with rwlock_t

Currently with the spinlock, all drivers are serialized(SMD_PKT,
BAM_DMUX etc.) when they try to log into the IPC logging even though the
drivers log into their own context space. The read/write lock will
enable multiple drivers to log into their context space in parallel.
This will help more in the case of drivers which are
performance-critical like BAM_DMUX.

ipc_log_context_list is read often and updated rarely so replace the
usage of spinlock_t with rwlock_t.

Change-Id: I91f18ef67b80edf6f045f93f51ad2f48e46b3bb4
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>