ROCK 5B: Use correct MAC address

The Rock 5B has only one network interface, which is PCIe based and has its own MAC address. It should avoid generating a MAC address from the RK3588 serial number, so that the MAC address stays the same between U-Boot and Linux.

assigned to @detlev

https://lore.kernel.org/u-boot/20240422135927.23582-1-detlev.casanova@collabora.com/

fwiw sounds like there should be some configuration for generate a mac on cpuid, to be disabled for rock5b then :) tbh i'm surprised it's just enabled on all rockchip boards

In some cases, there could be an error reading the MAC address from the network card, so you still want that fallback, that's why I think NET_PREFER_ROM_MAC_ADDR is better. Although, in a perfect world, NET_PREFER_ROM_MAC_ADDR should be the default and you could have a config NET_PREFER_ENV_MAC_ADDR for some reason