Merge remote-tracking branch 'remotes/ehabkost/tags/x86-next-pull-request' into staging

Merge remote-tracking branch 'remotes/ehabkost/tags/x86-next-pull-request' into staging

x86 MDS feature flags

md-clear and mds-no feature flags, for detection and mitigation
of MDS vulnerabilities (CVE-2018-12126, CVE-2018-12127,
CVE-2018-12130, CVE-2019-11091).

# gpg: Signature made Tue 21 May 2019 19:42:43 BST
# gpg:                using RSA key 2807936F984DC5A6
# gpg: Good signature from "Eduardo Habkost <ehabkost@redhat.com>" [full]
# Primary key fingerprint: 5A32 2FD5 ABC4 D3DB ACCF  D1AA 2807 936F 984D C5A6

* remotes/ehabkost/tags/x86-next-pull-request:
  target/i386: add MDS-NO feature
  docs: recommend use of md-clear feature on all Intel CPUs
  target/i386: define md-clear bit

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