docker-containerd: new package

docker-containerd: new package

docker-containerd is a daemon and API for controlling and managing runC
containers.

https://containerd.tools/

Signed-off-by: Christian Stewart <christian@paral.in>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
[Thomas:
 - simplify a bit the comments about the runtime dependencies
 - add missing comment on wchar, and take into account the BR2_USE_MMU
   dependency in the comment
 - factorize the build step with a foreach loop.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>