target/arm: Introduce gen_gvec_fn_arg_zzzz

Merge gen_gvec_fn_zzzz with the sve access check and the
dereference of arg_rrrr_esz.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220527181907.189259-37-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>