This driver probes available VirtIO MMIO devices on Qemu's virt platform and
exports the results in XML format via a ROM session. The exported ROM module
is suitable as configuration for the generic ARM platform driver.

This driver can currently recognize NIC, block, console, RNG, GPU, and
input devices. When a device of a given type is detected, it is assigned a
name based on its type and index on a bus. For example, if the system has
two VirtIO NIC devices, their names will be "nic0" and "nic1".

To simplify probing devices of the same type, each XML device node has
an additional "type" property node. The value of this property is simply
set to a string indicating device type, without any extra indices, e.g.,
"nic", "gpu", "input", etc.

! <device name="nic0">
!  <resource ... />
!  <property name="type" value="nic"/>
! </device>

Configuration
~~~~~~~~~~~~~

The virtdev_rom component appends the unmodified content of its own configuration
ROM to its output. This makes it possible to easily append extra policies
to the device configuration produced by the driver, e.g.,:

! <config>
!   <policy label_prefix="virtio_nic">  <device name="nic0">   </policy>
!   <policy label_prefix="virtio_kbd>   <device name="input0"> </policy>
!   <policy label_prefix="virtio_mouse> <device name="input1"> </policy>
! </config>
