fs/dcache.c: adaptive vfs_cache_pressure on suspend / resume

low vfs_cache pressure values save battery while idle, while
a low value also causes stutter with longer up times.
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>

Conflicts:
	fs/Makefile
	fs/sync.c