target/arm: Introduce gen_gvec_{ptr,fpst}_zzzz

Use these for the several varieties of floating-point
multiply-add instructions.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220527181907.189259-78-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>