ARM: dts: STiH407-pinctrl: Add pinctrl_rgmii1_mdio_1 node

On 96board, we can't reuse rgmii1-mdio as the pin pio1 3
( mdint ) is dedicated for user led green 1. So create
rgmii1_mdio_1 for 96board on which only mdio and mdc pins
are useful.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Peter Griffin <peter.griffin@linaro.org>