tests/functional: Have microblaze tests inherit common parent class

tests/functional: Have microblaze tests inherit common parent class

Have the MicroblazeMachine class being common to both
MicroblazeBigEndianMachine and MicroblazeLittleEndianMachine
classes. Move the xmaton and ballerina tests to the parent class.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250212123659.52764-11-philmd@linaro.org>
[thuth: Add missing ASSET statements to the leaf classes]
Signed-off-by: Thomas Huth <thuth@redhat.com>