target/arm: Implement TT instruction

Implement the TT instruction which queries the security
state and access permissions of a memory location.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1512153879-5291-8-git-send-email-peter.maydell@linaro.org
