armv8r64-extras/kas: Add tests.yml

tests.yml contains the Kas configuration for test suites. It works as an
additional configuration can be included, examples:

    kas build baremetal-linux.yml:tests.yml
    kas build virtualization.yml:tests.yml

Issue-Id: SCM-4357
Signed-off-by: Robbie Cao <robbie.cao@arm.com>
Change-Id: I72b2f95c7ea459513e5469fe6dd1c8a97f55ec3f