revert sync: export sync API symbols

This is needed to allow modules to link against the sync subsystem

Change-Id: I15c1818de329f24e4113ef1d0923413b22fd0eff
Signed-off-by: Erik Gilling <konkers@android.com>

Conflicts:
	drivers/base/sync.c (reverted from commit c0a2e1f94e8956e09b4cce252014f4a3f2db419a)