This makes all device emulations with a qdev drive property request
permissions on their BlockBackend. The only thing we block at this point
is resizing images for some devices that can't support it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>