This completes the set of integer narrowing saturating ops including:
     SQXTN, SQXTN2
     SQXTUN, SQXTUN2
     UQXTN, UQXTN2
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Message-id: 1394822294-14837-23-git-send-email-peter.maydell@linaro.org