gitlab-ci: Check building KVM-only aarch64 target

Add a manual new job to cross-build the aarch64 target with
only the KVM accelerator enabled (in particular, no TCG).

Re-enable running the similar job on the project Aarch64
custom runner.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Thomas Huth <thuth@redhat.com>