fs/dyn_sync_cntrl: dynamic sync control

The dynamic sync control interface uses new power_suspend interface

While screen is on, file sync is disabled
when screen is off, a file sync is called to flush all outstanding writes
and restore file sync operation as normal.

updated for 8974 kernels

Change-Id: I4cbf8ca1afdacccc35451587b4e24ba77847b657
Signed-off-by: Paul Reioux <reioux@gmail.com>