target/arm: Handle FPCR.AH in FMLSL (by element and vector)

target/arm: Handle FPCR.AH in FMLSL (by element and vector)

Handle FPCR.AH's requirement to not negate the sign of a NaN
in FMLSL by element and vector, using the usual trick of
negating by XOR when AH=0 and by muladd flags when AH=1.

Since we have the CPUARMState* in the helper anyway, we can
look directly at env->vfp.fpcr and don't need toa pass in the
FPCR.AH value via the SIMD data word.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250129013857.135256-31-richard.henderson@linaro.org
[PMM: commit message tweaked]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>