This was already set for 'sama5d27_som1_ek_mmc_defconfig' (first SD
card, full size). Without this option set, the MAC address is not read
from the I²C EEPROM at boot, and remains unset:

    U-Boot 2019.01 (Jan 01 2019 - 00:00:00 +0000)

    CPU: SAMA5D27 1G bits DDR2 SDRAM
    Crystal frequency:       24 MHz
    CPU clock        :      492 MHz
    Master clock     :      164 MHz
    DRAM:  128 MiB
    MMC:   sdio-host@a0000000: 0, sdio-host@b0000000: 1
    Loading Environment from FAT... OK
    In:    serial
    Out:   serial
    Err:   serial
    Net:
    Error: ethernet@f8008000 address not set.
    eth-1: ethernet@f8008000
    Hit any key to stop autoboot:  0
Signed-off-by: NAlexander Dahl <ada@thorsis.com>