development with QEMU, tips&tricks

Describe how QEMU can help develop a  LinuxBoot environment, allowing for quick reruns etc.
Include usage of `cpu`.

See also:
- https://www.kernel.org/pub/linux/kernel/people/will/docs/qemu/qemu-arm64-howto.md
- https://docs.u-boot.org/en/latest/develop/devicetree/dt_qemu.html

dump dtb:
```sh
qemu-system-riscv64 -M virt,dumpdtb=qemu-riscv.dtb
```