Merge remote-tracking branch 'remotes/vivier/tags/m68k-for-6.0-pull-request' into...

Merge remote-tracking branch 'remotes/vivier/tags/m68k-for-6.0-pull-request' into staging

Prepare MacOS ROM support:
  - add RTR instruction
  - fix unaligned access requirement
  - fix ATC bit (68040 MMU)

# gpg: Signature made Thu 11 Mar 2021 22:18:11 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-6.0-pull-request:
  target/m68k: add M68K_FEATURE_UNALIGNED_DATA feature
  target/m68k: reformat m68k_features enum
  target/m68k: don't set SSW ATC bit for physical bus errors
  target/m68k: implement rtr instruction

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