All of the U-Boot architectures have been switched to use these common
makefiles for their toolchain.

* cross/arm-none-eabi
* cross/aarch64-none-elf
* cross/riscv64-none-elf
* cross/mipsel-none-elf
* cross/powerpc-none-elf

powerpc and mipsel cross compilers are still using GCC 13.2 because
newlib for those platforms has K&R code for testing the linker and it
won't compile with a newer GCC. Upstream is working on that problem.

GDB for riscv64 has been added.

TODO: GDB python option fixes in PLIST