Revert "loop: use aio to perform io on the underlying file"

This reverts commit ebf33d126a54f4e84f7082faa2e73d0c60f526a3.
 lmk: Fine tune OOM for screen on/off

* Increase no. of parmeters handled by minfree
* Add interface to set different OOM values for screen on/off
* Add parameter to turn on/off auto set of different OOM values

Signed-off-by: klozz <xxx.reptar.rawrr.xxx@gmail.com>