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