usb: gadget: dummy_hcd: add SuperSpeed support

This patch adds SS support to the dummy hcd module.
It may be used to test SS device when no (SS) HW is
available.

USB 3.0 hub includes 2 hubs - one HS and one SS. This
patch adds support for a SS root hub in the dummy_hcd
module.

A new module parameter was added: is_super_speed. When
set to true, a SS root hub will also be registered and
the connected device will be enumerated over the SS
root hub. The default of this parameter is false.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

[ balbi@ti.com : slight change to commit log
		 fixed one coding style issue ]

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>