uwb: create a uwb bus type and add in-range peer devices to it

Documentation/usb/WUSB-Design-overview.txt states that UWB devices seen
by a UWB radio controller are added to /sys/bus/uwb/devices, but this
was not actually being done.  This functionality is needed in order for
UWB peer devices to be enumerated by user mode tools.  This patch
creates a uwb bus type and adds UWB peer devices to it as they are
discovered by the radio controller.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>