target/arm: Fix sign of sve_cmpeq_ppzw/sve_cmpne_ppzw

target/arm: Fix sign of sve_cmpeq_ppzw/sve_cmpne_ppzw

The normal vector element is sign-extended before
comparing with the wide vector element.

Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Message-id: 20180801123111.3595-2-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit df4e001093988544d09887122ae824f18ba55c68)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>