hw/ppc/pegasos2: Change device tree generation

hw/ppc/pegasos2: Change device tree generation

We generate a flattened device tree programmatically for VOF. Change
this to load the static parts from a device tree blob and only
generate the parts that depend on run time conditions such as CPU
type, memory size and PCI devices. Moving the static parts in a dts
makes the board code simpler and more generic.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/qemu-devel/383891fc2696609b27d2de9773efe1b4f493e333.1761176219.git.balaton@eik.bme.hu
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>