hw/ppc/e500: fix broken snapshot replay

hw/ppc/e500: fix broken snapshot replay

ppce500_reset_device_tree is registered for system reset, but after
c4b075318eb1 this function rerandomizes rng-seed via
qemu_guest_getrandom_nofail. And when loading a snapshot, it tries to read
EVENT_RANDOM that doesn't exist, so we have an error:

  qemu-system-ppc: Missing random event in the replay log

To fix this, use qemu_register_reset_nosnapshotload instead of
qemu_register_reset.

Reported-by: Vitaly Cheptsov <cheptsov@ispras.ru>
Fixes: c4b075318eb1 ("hw/ppc: pass random seed to fdt ")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1634
Signed-off-by: Maksim Kostin <maksim.kostin@ispras.ru>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>