hw/arm/sbsa-ref: Use two-stage SMMU

hw/arm/sbsa-ref: Use two-stage SMMU

Now that our SMMU model supports enabling both stages of translation
at once, we can enable this in the sbsa-ref board.  Existing guest
code that only programs stage 1 and doesn't care about stage 2 should
continue to run with the same behaviour, but guests that do want to
do nested SMMU configurations can now do so.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Message-id: 20240816161350.3706332-5-peter.maydell@linaro.org