target/arm: Implement MVE VADDLV

target/arm: Implement MVE VADDLV

Implement the MVE VADDLV insn; this is similar to VADDV, except
that it accumulates 32-bit elements into a 64-bit accumulator
stored in a pair of general-purpose registers.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210628135835.6690-15-peter.maydell@linaro.org