Make ScopedWakelock a shared library

Change the build configuration of multihal and its tests to make the
ScopedWakelock.cpp file and its associated headers available as a
library to be included by the fake subhals and the multihal binary
seperately.

Bug: 144722764
Test: Compiled and loaded onto device without issue
Change-Id: Ide83b6761302c5df6c72bc3202727341361b36ed