softfloat: Convert float128_silence_nan to parts

This is the minimal change that also introduces float128_params,
float128_unpack_raw, and float128_pack_raw without running into
unused symbol Werrors.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2 files changed