target/arm: Implement SVE Integer Reduction Group

Excepting MOVPRFX, which isn't a reduction.  Presumably it is
placed within the group because of its encoding.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180516223007.10256-10-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>