fs/dyn_sync_cntrl: dynamic sync control

The dynamic sync control interface uses Android kernel's unique early
suspend / lat resume 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.

Signed-off-by: Paul Reioux <reioux@gmail.com>
mm: Dynamic management of dirty page writebacks

This feature allows to have two different intervals for dirty page
writebacks and to dynamically manage them when the system has been
resumed (it's active) or when has been suspended.

Three new procfs parameters are exposed inside /proc/sys/vm path:
- "dynamic_dirty_writeback" is the activation status of this feature,
  set 1 to enable it, set 0 to disable it and use the standard behaviour
- "dirty_writeback_active_centisecs" is the interval for the dirty page
  writebacks when the system is active (screen on)
- "dirty_writeback_suspend_centisecs" is the interval for the dirty page
  writebacks when the system is suspended (screen off)

This feature is in part inspired on Francisco Franco's patch:
https://github.com/franciscofranco/mako/commit/34d79548cf16b69c7d0154836018e7f258a22947

Signed-off-by: Cristoforo Cataldo <cristoforo.cataldo@gmail.com>
Update kernel config
Fix dynamic sync