Merge remote-tracking branch 'remotes/sstabellini/tags/xen-20171026-tag' into staging

Merge remote-tracking branch 'remotes/sstabellini/tags/xen-20171026-tag' into staging

Xen 2017/10/26

# gpg: Signature made Thu 26 Oct 2017 23:57:16 BST
# gpg:                using RSA key 0x894F8F4870E1AE90
# gpg: Good signature from "Stefano Stabellini <stefano.stabellini@eu.citrix.com>"
# gpg:                 aka "Stefano Stabellini <sstabellini@kernel.org>"
# Primary key fingerprint: D04E 33AB A51F 67BA 07D3  0AEA 894F 8F48 70E1 AE90

* remotes/sstabellini/tags/xen-20171026-tag:
  xen: Log errno rather than return value
  xen: dont try setting max grants multiple times
  xen: add a global indicator for grant copy being available

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