target-arm: Enable the AArch32 ATS12NSO ops

Apply the correct conditions in the ats_access() function for
the ATS12NSO* address translation operations:
 * succeed at EL2 or EL3
 * normal UNDEF trap from NS EL1
 * trap to EL3 from S EL1 (only possible if EL3 is AArch64)

(This change means they're now available in our EL3-supporting
CPUs when they would previously always UNDEF.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1437751263-21913-5-git-send-email-peter.maydell@linaro.org