target/sparc: Fix FMUL8x16A{U,L}

target/sparc: Fix FMUL8x16A{U,L}

These instructions have f32 inputs, which changes the decode
of the register numbers.  While we're fixing things, use a
common helper for both insns, extracting the 16-bit scalar
in tcg beforehand.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20240502165528.244004-5-richard.henderson@linaro.org>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
(cherry picked from commit a859602c746baf4892cc8ca1ce003e92411d1716)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>