Merge remote-tracking branch 'remotes/rth/tags/pull-fpu-20180517' into staging

Merge remote-tracking branch 'remotes/rth/tags/pull-fpu-20180517' into staging

Roundup of softfloat patches

# gpg: Signature made Thu 17 May 2018 23:44:04 BST
# gpg:                using RSA key 64DF38E8AF7E215F
# gpg: Good signature from "Richard Henderson <richard.henderson@linaro.org>"
# Primary key fingerprint: 7A48 1E78 868B 4DB6 A85A  05C0 64DF 38E8 AF7E 215F

* remotes/rth/tags/pull-fpu-20180517: (28 commits)
  fpu/softfloat: Define floatN_silence_nan in terms of parts_silence_nan
  fpu/softfloat: Clean up parts_default_nan
  fpu/softfloat: Define floatN_default_nan in terms of parts_default_nan
  fpu/softfloat: Pass FloatClass to pickNaNMulAdd
  fpu/softfloat: Pass FloatClass to pickNaN
  fpu/softfloat: Make is_nan et al available to softfloat-specialize.h
  fpu/softfloat: Specialize on snan_bit_is_one
  fpu/softfloat: Remove floatX_maybe_silence_nan
  fpu/softfloat: Use float*_silence_nan in propagateFloat*NaN
  target/s390x: Remove floatX_maybe_silence_nan from conversions
  target/riscv: Remove floatX_maybe_silence_nan from conversions
  target/mips: Remove floatX_maybe_silence_nan from conversions
  target/m68k: Use floatX_silence_nan when we have already checked for SNaN
  target/hppa: Remove floatX_maybe_silence_nan from conversions
  target/arm: Remove floatX_maybe_silence_nan from conversions
  target/arm: Use floatX_silence_nan when we have already checked for SNaN
  fpu/softfloat: re-factor float to float conversions
  fpu/softfloat: Partial support for ARM Alternative half-precision
  target/arm: squash FZ16 behaviour for conversions
  target/arm: convert conversion helpers to fpst/ahp_flag
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>