ARM: dts: vf-colibri: add CLKOUT pin to pinctrl of FEC1

On the Colibri module, the RMII clock for the Ethernet PHY is
generated by the SoC. This patch adds that missing pin to the
pinctrl of FEC1. Because the boot loader initializes this pin,
ethernet worked even without this pin so far.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>