Make the binder_lock category optional

The binder_lock event type has been deprecated after binder
driver uses fine grained locking. This patch makes "binder_lock"
an optional category for atrace to support system w/ w/o FGL.

Bug: 37559846
Test: pixel phone with "atrace --async_start binder_lock"
Change-Id: I691efd355e903a26629f896a56a664502e5807f7