Solaris cannot be power offed with system_powerdown on qemu-system-sparc
Description of problem:
When a `system_powerdown` is done in the QEMU Monitor, nothing happens. Also happens with `qemu-system-sparc.exe` version 9.1.0-rc3, that is, it's not fixed in newer versions. Looking at [sun4m.c](https://gitlab.com/qemu-project/qemu/-/blob/master/hw/sparc/sun4m.c#L451) code, it registers a system_powerdown handler, but it's not working.
Steps to reproduce:
1. Start the machine with the command line above and wait for the complete OS initialization
2. Open the machine monitor
3. Do a `system_powerdown` command
4. Nothing will happen
Additional information: