usb: Add USB 3.1 Precision time measurement capability descriptor support

BugLink: http://bugs.launchpad.net/bugs/1519623



USB 3.1 devices that support precision time measurement have an
additional PTM cabaility descriptor as part of the full BOS descriptor

Look for this descriptor while parsing the BOS descriptor, and store it in
struct usb_hub_bos if it exists.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit faee822c)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>