ARM: dts: gemini: ssi1328: permit to use gigabit

I believed that gigabit was not working due to unknown missing GPIO.
But the problem was due to Marvell PHY incorrectly setting delay.
Now it is fixed, gigabit works.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>