tests/functional: test device passthrough on aarch64

tests/functional: test device passthrough on aarch64

This test allows to document and exercise device passthrough, using a
nested virtual machine setup. Two disks are generated and passed to the
VM, and their content is compared to original images.

Guest and nested guests commands are executed through two scripts, and
init used in both system is configured to trigger a kernel panic in case
any command fails. This is more reliable and readable than executing all
commands through prompt injection and trying to guess what failed.

Initially, this test was supposed to test smmuv3 nested emulation
(combining both stages of translation), but I could not find any setup
(kernel + vmm) able to do the passthrough correctly, despite several
tries.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-id: 20250627200222.5172-1-pierrick.bouvier@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>