usb: xhci: Make some static functions global

This patch makes some static functions global to avoid duplications
in different files. These functions can be used in the implementation
of xHCI debug capability. There is no functional change.

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