target/arm: Handle FPCR.AH in vector FCMLA

target/arm: Handle FPCR.AH in vector FCMLA

The negation step in FCMLA mustn't negate a NaN when FPCR.AH
is set. Handle this by passing FPCR.AH to the helper via the
SIMD data field, and use this to select whether to do the
negation via XOR or via the muladd negate_product flag.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250129013857.135256-26-richard.henderson@linaro.org
[PMM: Expanded commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>