[lantiq] add missing pinmux patch

Fix lantiq pinmux which affected PCI and USB.

Known affected boards are: ARV4518 and ARV7518.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt@36312 3c298f89-4303-0410-b956-a3cf2f4a3e73