target/arm: Handle FPCR.AH in SVE FCMLA

target/arm: Handle FPCR.AH in SVE FCMLA

The negation step in SVE FCMLA mustn't negate a NaN when FPCR.AH is
set.  Use the same approach as we did for A64 FCMLA of passing in
FPCR.AH and using it to select whether to negate by XOR or by the
muladd negate_product flag.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250129013857.135256-28-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>