SF: Simplify layer tracing

As preparation to support transaction tracing, do the
following:
1. refactor the ring buffer code so it can be reused
2. remove layer async tracing since we will use
transaction tracing for always on tracing

Test: presubmit
Test: capture sf trace via bugreport
Bug: 200284593

Change-Id: I28388c6db27a420c078e1cc33b0b378c55c6c5d6