-machine raspi4b won't dump dtb
Description of problem:
the raspi4b machine won't dump tdb
Steps to reproduce:
```
$ qemu-system-aarch64 -machine virt -machine dumpdtb=p.dmp
qemu-system-aarch64: info: dtb dumped to p.dmp. Exiting.
$ qemu-system-aarch64 -machine raspi4b -machine dumpdtb=p.dmp
```
notice no dtb is dumped for the raspi4b machine
Additional information:
see also https://gitlab.com/qemu-project/qemu/-/issues/2729