ARM: dts: meson8b: odroidc1: use the MAC address stored in the eFuse

Odroid-C1 uses the MAC address stored in eFuse at offset 0x1b4 (which is
defined as a "standard" offset for all Meson8 and Meson8b boards, but
testing shows that MXQ doesn't have the eFuse values programmed and
EC-100 stores it's MAC address in eMMC).

Add the nvmem cell which points to the MAC address and asssign it to the
Ethernet controller as "mac-address".
As result of this the MAC address which is stored in the eFuse is now
assigned to the Ethernet controller and consistent across reboots.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>