Asynchronous Fsync: initial extraction of Async Fsync from HTC

Change-Id: I12c566344cd4670137385d6ccd73cb7747b7e901
Signed-off-by: Paul Reioux <reioux@gmail.com>
defconfig: enable ASYNC_FSYNC

Change-Id: I2a4914f77cad162ff0599c3fbc05ab5493a6e53c