This patch adds SuperSpeed descriptors to the
g_zero gadget.

The SuperSpeed descriptors were added both for
f_soursesink and f_loopback function drivers.
Signed-off-by: NTatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: NAmit Blay <ablay@codeaurora.org>
Signed-off-by: NFelipe Balbi <balbi@ti.com>