Mostly refactoring, with the exception that USB_PORT_STAT_L1 link state
is reported if xhci port link is in U2 AND port is powered.

Previously we did not check if the port was powered, but according to
xhci spec 4.19.1.1.6 All the 'Enabled' states, including
USB_PORT_STAT_L1 (U2), U1, U0 and U3 must have Port power bit set.
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>