ARM: dts: sun7i: olinuxino-micro: Enable the EMAC

The A20-olinuxino-micro has the EMAC wired in. Enable it in the DT so
that we can use it.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Olof Johansson <olof@lixom.net>