Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

Bugfixes, and reworking of the atomics documentation.

# gpg: Signature made Mon 13 Apr 2020 07:56:22 BST
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream:
  module: increase dirs array size by one
  memory: Do not allow direct write access to rom_device regions
  vl.c: error out if -mem-path is used together with -M memory-backend
  rcu: do not mention atomic_mb_read/set in documentation
  atomics: update documentation
  atomics: convert to reStructuredText
  oslib-posix: take lock before qemu_cond_broadcast
  piix: fix xenfv regression, add compat machine xenfv-4.2

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