virtio,vhost,pc: features, fixes, cleanups.

Virtio 1.0 support for virtio-mmio.
Misc fixes, cleanups.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

# gpg: Signature made Mon 16 Sep 2019 16:17:30 BST
# gpg:                using RSA key 281F0DB8D28D5469
# gpg: Good signature from "Michael S. Tsirkin <mst@kernel.org>" [full]
# gpg:                 aka "Michael S. Tsirkin <mst@redhat.com>" [full]
# Primary key fingerprint: 0270 606B 6F3C DF3D 0B17  0970 C350 3912 AFBE 8E67
#      Subkey fingerprint: 5D09 FD08 71C8 F85B 94CA  8A0D 281F 0DB8 D28D 5469

* remotes/mst/tags/for_upstream:
  virtio-mmio: implement modern (v2) personality (virtio-1)
  virtio pmem: user document
  intel_iommu: Remove the caching-mode check during flag change
  pc/q35: Disallow vfio-pci hotplug without VT-d caching mode
  qdev/machine: Introduce hotplug_allowed hook
  intel_iommu: Sanity check vfio-pci config on machine init done
  backends/vhost-user.c: prevent using uninitialized vqs
  vhost-user-blk: prevent using uninitialized vqs
  docs/nvdimm: add example on persistent backend setup
  MAINTAINERS: update virtio-rng and virtio-serial maintainer

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