target/arm: Handle FPCR.AH in SVE FTMAD

target/arm: Handle FPCR.AH in SVE FTMAD

The negation step in the SVE FTMAD insn mustn't negate a NaN when
FPCR.AH is set.  Pass FPCR.AH to the helper via the SIMD data field,
so we can select the correct behaviour.

Because the operand is known to be negative, negating the operand
is the same as taking the absolute value.  Defer this to the muladd
operation via flags, so that it happens after NaN detection, which
is correct for FPCR.AH.

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