ARM: dts: imx28-evk: add missing properties for fec

Add missing properties for fec, phy-supply, phy-reset-gpios and
phy-reset-duration, which are required by fec driver for successfully
probe fec from device tree, if bootloader hasn't set those things up.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>