virtualization: Add virtio-video driver as external module.

virtualization: Add virtio-video driver as external module.

This driver should conform WIP spec v3 [1] with some updates for spec v4
[2], and, some unspecified features such as VIRTIO_VIDEO_DEVICE_CAMERA.

Imported from internal OpenSynergy's revision:

  bcc33b6b9e0156b381a70c54d2df02c57b63d270

Kernel was configured with necessary features for this driver:

  enable MEDIA_SUPPORT
  disable MEDIA_SUBDRV_AUTOSELECT
  enable MEDIA_PLATFORM_SUPPORT
  enable VIDEO_VIRTIO

Keep driver as an external module to simplify future updates.

[1]: https://lists.oasis-open.org/archives/virtio-dev/202002/msg00002.html
[2]: https://lists.oasis-open.org/archives/virtio-dev/202006/msg00072.html

Bug-AGL: SPEC-4148
Change-Id: Iea339194b22443f67b3e2ffddca84118357a2f15
Signed-off-by: Vasyl Vavrychuk <vasyl.vavrychuk@opensynergy.com>