target-arm: Add Hyp mode checks to bad_mode_switch()

We don't actually support Hyp mode yet, but add the correct
checks for it to the bad_mode_switch() function for completeness.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Sergey Fedorov <serge.fdrv@gmail.com>
Message-id: 1455556977-3644-8-git-send-email-peter.maydell@linaro.org
