Vold: Add the fstrim subsystem to vold

The fstrim subsystem implements the dotrim command, which goes
through all the writable filesystems on the device, and invokes
the FITRIM ioctl() on them.  This marks all the unused blocks on
the underlying flash device as unused, so the device performs better.

Change-Id: I5fc8c2f60e0bc823f162d0f89580fb288ecb2160

Conflicts:
	Android.mk
	CommandListener.cpp
	CommandListener.h
	fstrim.c

	modified:   Android.mk
	modified:   CommandListener.cpp
	modified:   CommandListener.h
	modified:   fstrim.c