USB: android: Provide sysfs file for enabling remote wakeup capability

USB device can specify remote wakeup capability in the configuration
descriptor.  Host may select remote wakeup feature before suspending
the device.  Remote wakeup capability is disabled by default in
android gadget.  Provide sysfs file for enabling remote wakeup capability.
User space can enable/disable this capability based on the selected
composition.  This will also allow testing suspend/resume chapter 9 tests
with remote wakeup enabled.

Change-Id: Ib24aa6c05ace697564ebe5940e62e8f65db4d7c3
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>