Merge remote-tracking branch 'remotes/aperard/tags/pull-xen-20201020' into staging

Merge remote-tracking branch 'remotes/aperard/tags/pull-xen-20201020' into staging

Xen queue

* cleanup patches.
* improve xen backend setup performance when other xen guests are
  running/booting.
* improve xen guest migration when running in a stubdomain.

# gpg: Signature made Tue 20 Oct 2020 10:55:11 BST
# gpg:                using RSA key F80C006308E22CFD8A92E7980CF5572FD7FB55AF
# gpg:                issuer "[email protected]"
# gpg: Good signature from "Anthony PERARD <[email protected]>" [marginal]
# gpg:                 aka "Anthony PERARD <[email protected]>" [marginal]
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 5379 2F71 024C 600F 778A  7161 D8D5 7199 DF83 42C8
#      Subkey fingerprint: F80C 0063 08E2 2CFD 8A92  E798 0CF5 572F D7FB 55AF

* remotes/aperard/tags/pull-xen-20201020:
  hw/xen: Set suppress-vmdesc for Xen machines
  xen-bus: reduce scope of backend watch
  xen: Rename XENBACKEND_DEVICE to XENBACKEND
  xen: xenguest is not used so is not needed

Signed-off-by: Peter Maydell <[email protected]>