USB: gadget: f_mass_storage: Fix USB WHQL Certification Issues

As part of the USB MSCV testing, the host issues random commands and
expects the device to respond, but the device is not able to respond
to these commands, since the endpoints are not enabled due to the
thread latency and hence the compliance testing is failing.  Hence
enabling/disabling the endpoints in interrupt context.

This change fixes device panic issue where mass storage thread gets
schedule late enough and try to disable USB endpoint when USB controller
driver is already into low power mode.

Change-Id: I27ad5875a3bde9a480866173d18cc3292c4af969
Signed-off-by: Chiranjeevi Velempati <cvelempa@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>