Add rk3588 support
The RESF was kind enough to provide me with 3 ARM SBCs to "put" Rocky Linux on. As time has passed on and daily driving these, I am now confident that the current software support in upstream is "good for prod".
This PR adds support for the boards on which I have booted Rocky Linux and verified that the hardware works. With one exception: The single USB port on the FriendlyElec NanoPC-T6 does not yet work. It is expected to work in later releases of U-Boot. But hey, NVMe works flawlessly on all 3 boards! ;)