tests: Add descriptors for QCOW2 format firmware builds

tests: Add descriptors for QCOW2 format firmware builds

Now that we ignore all firmwares that are not in raw format
while performing autoselection, we can have descriptors for
firmware builds in QCOW2 format without breaking anything.

Note that the descriptors are arranged so that they have the
highest priority on aarch64, but the lowest one on x86_64.
This matches the expectation that QCOW2 will quickly be
adopted as the default on aarch64, where its use produces
significant benefits in terms of memory usage, while x86_64
will likely stick with raw for the foreseeable future.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>