libsync: add support to new Sync API

Change libsync functions in a way that it can run dynamically on both
APIs.

v2: fix whitespace changes and poll return handling

v3: handle error cases on sync_wait()

Test: Sync unit tests still passes.
Change-Id: I743ab92ce39cbfa75dca41dd0a435efa9f2aab66
hange-Id: Ib56f2c6441b41028bc9f66998676790b7713988a