MIPS: lantiq: enable pci clk conditional for xrx200 SoC

The xrx200 SoC family has the same PCI clock register layout as the AR9.
Enable the same quirk as for AR9

Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4235/