Add fstrim support to restore NAND/eMMC write performance. fstrim applet is a port from util-linux.

"Trimming" your NAND/eMMC storage will restore the write performance back to normal
after having slow down issues on sequential write and random write due to usage over time.

Good reading on subject: http://forum.xda-developers.com/showthread.php?t=1971852

Change-Id: I0ba903cb7248b288152736f2e3392a5bdbe77ba3
update config (fstrim addition)

Change-Id: I5c872afbcd071d389d0db3f10862677c08212e2c
Merge remote-tracking branch 'origin/cm-10.1' into cm-10.1-linaro