target/arm: SVE brk[ab] merging does not have s bit

target/arm: SVE brk[ab] merging does not have s bit

While brk[ab] zeroing has a flags setting option, the merging variant
does not.  Retain the same argument structure, to share expansion but
force the flag zero and do not decode bit 22.

Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20181226215003.31438-1-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>