Merge remote-tracking branch 'remotes/rth/tags/pull-softfloat-20181104' into staging

Only use divdeu insn with Power7 and later.

# gpg: Signature made Sun 04 Nov 2018 10:05:50 GMT
# 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-softfloat-20181104:
  softfloat: Don't execute divdeu without power7

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