Add SIOplus I/O scheduler

SIOplus is based on SIO, but has some slight modifications:
- The starved write requests counter only counts when there actually
  are write requests in the queue
- Fixed the bug that the writes_starved were not initialized on init
- Implemented new tuneables
SIOplus tuning

Change-Id: Id6c4717b215477866d0668d6de2085fe6329fd6a
Bump kernel version to 0.334

Change-Id: I2b682211e02e8152aad5ab7203c183f2357fa725