SF: add trace points for dispatcher system

Adds initial tracing points for the dispatcher and predictor vsync
signal dispatch system, along with some helper classes to turn traces
on and off based on system properties.

Verbose tracing can be turned on with 'setprop debug.sf.vsp_trace 1'

Test: boot with tracepoints on, see intended traces
Bug: 144927823

Change-Id: Ib6764404b77881887f338a41a25daa1d7068dc1f