content: Reserve device ID 49 for Virtio Media

[aesteve-rh]

Virtio Media can handle video encoders, decoder, and capture devices to be exposed to the guest.
The device can almost transparently handle v4l2-compatible devices in the host.

Here is the patch with the request. Device ID 48 has been reserved for Virtio USB (#193).

[mstsirkin]

BALLOT CREATED AT URL: https://groups.oasis-open.org/higherlogic/ws/public/ballot?id=3850