iotests: test m68k with the virt machine

This allows to cover the virtio tests with a 32bit big-endian
virtio-mmio machine.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20210319202335.2397060-6-laurent@vivier.eu>
Message-Id: <20210323165308.15244-21-alex.bennee@linaro.org>

tests/qemu-iotests/testenv.py

@@ -208,6 +208,7 @@ def __init__(self, imgfmt: str, imgproto: str, aiomode: str,
             ('arm', 'virt'),
             ('aarch64', 'virt'),
             ('avr', 'mega2560'),
+            ('m68k', 'virt'),
             ('rx', 'gdbsim-r5f562n8'),
             ('tricore', 'tricore_testboard')
         )