Added functions for open using USB file descriptor

Android USB api provides file descriptor. This can
be utilised to make a libusb device. Libusb has been
adequately modified to utilise fd. Added functions which
to use corresponding libusb functions.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>
Added usb_open_dev_fd for opening on android

Open using provided file descriptor. This function was
earlier left out. One crucial point is not to close
the USB device ( which is done normally by libftdi).
Nor try to open it again. It is already open.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>