Add the support for AIDR register. It currently advertises
SMMU V3.0 spec.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200728150815.11446-10-eric.auger@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>