target/arm: Honour FPCR.AH=1 default NaN value in FMAXNMQV, FMINNMQV

target/arm: Honour FPCR.AH=1 default NaN value in FMAXNMQV, FMINNMQV

The FMAXNMQV and FMINNMQV insns use the default NaN as their identity
value for inactive source vector elements. We open-coded this in
sve_helper.c, hoping to avoid a function call. However, this fails
to account for FPCR.AH=1 changing the default NaN value to set the
sign bit. Use a call to floatN_default_nan() to obtain this value.

Fixes: 1de7ecfc12d05 ("target/arm: Implement FADDQV, F{MIN, MAX}{NM}QV for SVE2p1")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250718173032.2498900-10-peter.maydell@linaro.org