CAN, GPIO, RNG vhost-devices for virtio-loopback [v6]

CAN, GPIO, RNG vhost-devices for virtio-loopback [v6]

This patch adds key components of the viritio-loopback architecture:
- kernel-module-virtio-loopback: the virtio loopback kernel driver
- CAN, GPIO and RNG vhost-user devices from meta-virtualization (commit a215d8320edee0a317a6511e7e2efa5bba867486)

Notes:
- libgpiod, comes from meta-openembedded commit 3029554ceb0b0bb52a8d8ec3f0a75c5113662fe6
- cleaned eg-virt from unused drivers (kernel-module-virtio-video)

Bug-AGL: SPEC-4834

V2 changes:
- related meta-virtualization commit message added in the cover letter
- updated libgpio recipe to v2.1
- SPEC reference added in cover letter

v3
- add vhost-device-can preliminary version. This is placed here with
  the objective to share the link when proposing the new device to
  the rust-vmm/vhost-device community
- remove cargo-update-recipe-crates includes in bb file because it is
  not supported by the rust mixin layer
- vhost-device folder README changes

v4
- fixed libgpiod required version
- tested ref hw and qemu x86/64 builds
- vsock, scsi and i2c rust devices removed from the build as they
  are not yet integrated in virtiod-loopback
- cleaned-up kernel modules kernel-module-virtio-video and
  gstreamer1.0-plugins-bad
- virtio-loopback-driver set to 2-or-later

v5
- Merge with Jan-Simon version v4:
   - remove broken kernel-module-virtio-video
   - use FEATURE_PACKAGES instead of IMAGE_INSTALL:append
   - rename virtio-loopback-driver.bb to
     kernel-module-virtio-loopback_git.bb for consistency

v6
- adding version in the title
- removing MODULE_GIT_REPOSITORY in kernel-modules

Change-Id: Id6cc58e777b9edad03b6c50d0dddaac8601edeaf
Signed-off-by: Michele Paolino <m.paolino@virtualopensystems.com>
Signed-off-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>