libsync: open new location of sw_sync file

sw_sync file for debug was moved to debugfs. Try to open it and if it
fails try to open /dev/sw_sync.

Test: Sync unit tests still passes.
Change-Id: Ie078fbc2eb5294f28b916a9e65b7fcd3a18a8580
hange-Id: I216874964368d939bed2779d98cd89e527a57d45