tests/avocado/machine_aspeed.py: Add eMMC boot tests

tests/avocado/machine_aspeed.py: Add eMMC boot tests

The image was built using the process described in commit c8cb19876d3e
("hw/sd/sdcard: Support boot area in emmc image") with artefacts from
the latest successful build of the IBM P10 BMC platform available on:

  https://jenkins.openbmc.org/job/ci-openbmc/distro=ubuntu,label=docker-builder,target=p10bmc/lastSuccessfulBuild/

Signed-off-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>