ARM: dts: exynos: Add a placeholder for a MAC address

Add a placeholder for a MAC address. A bootloader may fill it
to set the MAC address and override EEPROM settings.

Signed-off-by: Łukasz Stelmach <l.stelmach@samsung.com>
Link: https://lore.kernel.org/r/20201001135254.28178-1-l.stelmach@samsung.com


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>