mipsel malta machine is broken in avocado console tests
Description of problem:
As noted in #1884 we see failures of the boot_linux_console.py test. Unlikely other avocado failures, these ones are consistent and reproduce locally with 100% success

```
./configure --target-list=mipsel-softmmu
make -j 20
cd build
./pyvenv/bin/python3 -B -m avocado --show=app run --job-results-dir=./tests/results -t arch:mipsel --failfast tests/avocado/boot_linux_console.py:BootLinuxConsole.test_mips_malta32el_nanomips_4k
```

This test will reliably fail with a timeout waiting for console output.

Attempting to run the QEMU command manually

```
$ ./qemu-system-mipsel -display none -vga none -machine malta -chardev stdio,id=console -serial chardev:console -cpu I7200 -no-reboot -kernel /home/berrange/src/virt/qemu/build/tests/results/job-2023-09-13T17.14-77de093/test-results/tmp_dir520smana/1-tests_avocado_boot_linux_console.py_BootLinuxConsole.test_mips_malta32el_nanomips_4kkernel -append 'printk.time=0 mem=256m@@0x0 console=ttyS0'
```

results in no serial console output at all.

IMHO either the MIPS malta machine has had a regression, or the kernel we're downloading for testing has had a regression.
Additional information: