Change maintainer for Avionic Design boards

I no longer work for Avionic Design and don't have access to hardware,
so I'll pass on maintainership to Alban.

Acked-by: Alban Bedel <alban.bedel@avionic-design.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>