usb: android: f_uvc: Add support for UVC function

Integrate USB video class function driver with android
gadget. User can run below sample commands to enumerate
UVC as webcam on hosts:

->setprop sys.usb.config none
->echo 0 > /sys/class/android_usb/android0/enable
->echo $PID > /sys/class/android_usb/android0/idProduct
->echo video > /sys/class/android_usb/android0/functions
->echo 1 > /sys/class/android_usb/android0/enable

After above commands user should start userspace application
to open video device and handle v4l2 control requests. USB
enumeration is disabled until then.

CRs-fixed: 1097684
Change-Id: Ib147959dd8ca4bf6230b1a6adbed67198e0c56bb
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>