Merge remote-tracking branch 'remotes/vivier/tags/m68k-for-5.0-pull-request' into staging

Fix m68k single-stepping with remote gdb

# gpg: Signature made Tue 21 Jan 2020 12:21:12 GMT
# gpg:                using RSA key CD2F75DDC8E3A4DC2E4F5173F30C38BD3F2FBE3C
# gpg:                issuer "laurent@vivier.eu"
# gpg: Good signature from "Laurent Vivier <lvivier@redhat.com>" [full]
# gpg:                 aka "Laurent Vivier <laurent@vivier.eu>" [full]
# gpg:                 aka "Laurent Vivier (Red Hat) <lvivier@redhat.com>" [full]
# Primary key fingerprint: CD2F 75DD C8E3 A4DC 2E4F  5173 F30C 38BD 3F2F BE3C

* remotes/vivier/tags/m68k-for-5.0-pull-request:
  m68k: Fix regression causing Single-Step via GDB/RSP to not single step

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