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

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

Handle the FPCR.AH semantics that we do not change the sign of an
input NaN in the FRECPS and FRSQRTS scalar insns, by providing
new helper functions that do the CHS part of the operation
differently.

Since the extra helper functions would be very repetitive if written
out longhand, we condense them and the existing non-AH helpers into
being emitted via macros.

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