ARM: BCM53016: MR32: get mac-address from nvmem

The MAC-Address of the MR32's sole ethernet port is
located in offset 0x66 of the attached AT24C64 eeprom.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>