Merge remote-tracking branch 'remotes/vivier/tags/m68k-for-2.12-pull-request' into staging

# gpg: Signature made Tue 20 Mar 2018 09:07:55 GMT
# gpg:                using RSA key F30C38BD3F2FBE3C
# gpg: Good signature from "Laurent Vivier <lvivier@redhat.com>"
# gpg:                 aka "Laurent Vivier <laurent@vivier.eu>"
# gpg:                 aka "Laurent Vivier (Red Hat) <lvivier@redhat.com>"
# Primary key fingerprint: CD2F 75DD C8E3 A4DC 2E4F  5173 F30C 38BD 3F2F BE3C

* remotes/vivier/tags/m68k-for-2.12-pull-request:
  target/m68k: add a mechanism to automatically free TCGv
  target/m68k: add DisasContext parameter to gen_extend()

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