on single core Raspberry Pi, qemu-system-sparc appears to hang in bios
Description of problem:
I suspect it to be a race condition related to running on the slow single core Raspberry Pi, as I haven't managed to reproduce on x86 even when using taskset to tie qemu to a single core.

The problem occurs about 4 out of 5 runs on qemu 5.2 (raspbian bullseye) and so far 100% of the time on qemu 6.1.

About five seconds after start the sparc bios gets as far as `ttya initialized` and then appears to hang indefinitely.

Instead, it should continue after about 3 more seconds with:
```
Probing Memory Bank #0 32 Megabytes
Probing Memory Bank #1 Nothing there
Probing Memory Bank #2 Nothing there
Probing Memory Bank #3 Nothing there
```

See below for workaround.
Steps to reproduce:
1. Need a single core Raspberry Pi running raspbian, such as Raspberry Pi 1 or Zero
2. Download ss5.bin from https://github.com/andarazoroflove/sparc/raw/master/ss5.bin
3. Run the command:
```
qemu-system-sparc -m 32 -bios ss5.bin -nographic
```
After about 5 seconds of output it hangs at `ttya initialized`
Additional information:
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