usb: gadget: Add function wakeup support

USB 3.x allows functions to be independently suspended for better
power management on a per-interface basis. Additionally a function
can also be a remote wake source. Add support for allowing a
function to issue a remote wakeup to the composite driver, which in
turn will issue a device notification packet request to the device
controller driver.

Change-Id: I72b3a25cfffa6060f1e10479e3c0ad9c0409aa45
Signed-off-by: Jack Pham <jackp@codeaurora.org>