dt-bindings: virtio: Add binding for virtio devices

Allow virtio device sub-nodes to be added to the virtio mmio or pci
nodes. The compatible property for virtio device must be of the format
"virtio,device<ID>", where ID is virtio device ID in hexadecimal format.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/d8319fd18df7086b12cdcc23193c313893aa071a.1627362340.git.viresh.kumar@linaro.org


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Rob Herring <robh@kernel.org>