rk3399: r4s: Derive local MAC address if EEPROM is missing

rk3399: r4s: Derive local MAC address if EEPROM is missing

Some RK3399 boards, such as newer revisions of NanoPi R4S, do not
provide an EEPROM chip containing a globally unique MAC address.

Currently, this means that a randomly generated temporary MAC address
may be generated each time the device is rebooted, leading to ARP cache
issues and other confusing bugs.

Since RK3399 CPUs provide a built-in unique serial number, we can
reliably derive a locally MAC address from it by reading the
corresponding bits from the non-secure efuse block.

Enable configuration options that allow deriving a local MAC address
from the CPU serial number.