Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-3.0-pull-request...

Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-3.0-pull-request' into staging

Some ppc/ppc64 fixes:
- we can run now most of the targets on a ppc64 host with 64kB pages
- add swapcontext syscall to run tests/test-coroutine in
  debian-powerpc-user-cross

# gpg: Signature made Mon 23 Jul 2018 13:55:57 BST
# 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/vivier2/tags/linux-user-for-3.0-pull-request:
  linux-user/ppc: Implement swapcontext syscall
  linux-user: fix ELF load alignment error

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