tests/functional: Convert the microblaze avocado tests into standalone tests

tests/functional: Convert the microblaze avocado tests into standalone tests

The machine_microblaze.py file contained two tests, one for each
endianness. Since we only support one QEMU target binary per file
in the new functional test environment, we have to split this file
up into two files now.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240830133841.142644-23-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>