board: amlogic: vim3: read ethernet MAC address from efuse

Add the board specific code for reading built-in ethernet MAC address
from efuse.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>