xhci: Move xhci_pme_quirk() behind #ifdef CONFIG_PM

xhci_pme_quirk() is only used when CONFIG_PM is defined.
Compiling a kernel without PM complains about this function

[reworded commit message -Mathias]
Cc: <stable@vger.kernel.org>
Signed-off-by: Tomer Barletz <barletz@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>