ADB sideload command not work

In kernel(3.10) USB ADB gadget driver is removed.
Using Functionfs for USB adb gadget.

Android recovery uses a stripped down version
of adb command for sideload only. It's missing
the ffs function support, so add the ffs
support to allow sideload command to work

b/12608946

Change-Id: I4ad024723dfc5bdb544548391f99637c390b171e
Signed-off-by: Pierre Couillaud <pierre@broadcom.com>