usb: gadget: Perform usb_ep_disable in workqueue

bam_data_disconnect can be called in interrupt context,
as a result of suspend event. During an interrupt
handling, usb gadget lock is held, so when trying
to disable an endpoint a deadlock happens.
This fix moves the disabling of the data endpoints to
a deferred context, which prevents the deadlock.

Change-Id: I4caf0740842760630aac6649b7fe7ed93a940e7a
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>