ANDROID: Avoid taking multiple locks in handle_lmk_event

Conflicting lock events have been reported resulting from
rcu_read_lock, mmap_sem (in get_cmdline) and  lmk_event_lock.

This CL avoids the possibility of these conditions by moving
handle_lmk_event outside rcu_read_lock and invoking get_cmdline before
lmk_event_lock is taken.

Bug: 133479338, 133829075
Signed-off-by: Jim Blackler <jimblackler@google.com>
Change-Id: Ib3c32587472bd972e3ac108798e2af3f4a5c329a