usb: xhci: hack xhci_urb_enqueue to support hid.mousepoll behaviour

xHCI creates endpoint contexts directly from the device's endpoint
data, so submitting URBs with urb->interval different from the hardware
interval has no effect.

Add an explicit reconfiguration of the endpoint context when requested,
which will happen only when the interval is different from the cached
value. In practice, the reconfiguration only happens on the first URB
submitted for the endpoint.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.org>