Merge remote-tracking branch 'remotes/awilliam/tags/vfio-update-20210618.0' into staging

VFIO update 2021-06-18

 * VFIO migration documentation (Tarun Gupta)

 * Fix SaveVMHandler de-registration (Kunkun Jiang)

 * Fix vmstate change transition (Kirti Wankhede)

# gpg: Signature made Fri 18 Jun 2021 16:20:34 BST
# gpg:                using RSA key 42F6C04E540BD1A99E7B8A90239B9B6E3BB08B22
# gpg:                issuer "alex.williamson@redhat.com"
# gpg: Good signature from "Alex Williamson <alex.williamson@redhat.com>" [full]
# gpg:                 aka "Alex Williamson <alex@shazbot.org>" [full]
# gpg:                 aka "Alex Williamson <alwillia@redhat.com>" [full]
# gpg:                 aka "Alex Williamson <alex.l.williamson@gmail.com>" [full]
# Primary key fingerprint: 42F6 C04E 540B D1A9 9E7B  8A90 239B 9B6E 3BB0 8B22

* remotes/awilliam/tags/vfio-update-20210618.0:
  vfio/migration: Correct device state from vmstate change for savevm case
  vfio: Fix unregister SaveVMHandler in vfio_migration_finalize
  docs/devel: Add VFIO device migration documentation

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