target/arm: Handle FPCR.AH in FRECPS and FRSQRTS vector insns

target/arm: Handle FPCR.AH in FRECPS and FRSQRTS vector insns

Handle the FPCR.AH "don't negate the sign of a NaN" semantics
in the vector versions of FRECPS and FRSQRTS, by implementing
new vector wrappers that call the _ah_ scalar helpers.

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