tests/avocado: tag sbsa tests as tcg only

As firmware runs at a higher privilege level than the hypervisor we
can only run these tests under TCG emulation.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231201093633.2551497-6-alex.bennee@linaro.org>

tests/avocado/machine_aarch64_sbsaref.py

@@ -20,6 +20,10 @@ class Aarch64SbsarefMachine(QemuSystemTest):
     """
     :avocado: tags=arch:aarch64
     :avocado: tags=machine:sbsa-ref
+    :avocado: tags=accel:tcg
+
+    As firmware runs at a higher privilege level than the hypervisor we
+    can only run these tests under TCG emulation.
     """
 
     timeout = 180