xhci: debugfs: add debugfs interface to enable compliance mode for a port

Enable compliance transition for a port by writing "compliance" to the
ports portsc file in debugfs.
port must be "Not-connected" and Link must be in RxDetect state to enable
compliance mode.

Only needed for host that have CTC flag set.
Allows state transitioning to compliance at 1st LFPS timeout.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>