target/arm: Tidy SQDMULH, SQRDMULH (vector)

target/arm: Tidy SQDMULH, SQRDMULH (vector)

We already have a gvec helper for the operations, but we aren't
using it on the aa32 neon side.  Create a unified expander for
use by both aa32 and aa64 translators.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20240528203044.612851-31-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>