ramips: add i2c pingroup to the pinmux for rt-n14u

i2c pins are wired to wps a reset button

Signed-off-by: Pavel Löbl <lobl.pavel@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43985 3c298f89-4303-0410-b956-a3cf2f4a3e73