target/arm: Create gen_gvec_{u,s}{rshr,rsra}

target/arm: Create gen_gvec_{u,s}{rshr,rsra}

Create vectorized versions of handle_shri_with_rndacc
for shift+round and shift+round+accumulate.  Add out-of-line
helpers in preparation for longer vector lengths from SVE.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200513163245.17915-3-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>