MAINTAINERS: Extend info, add wiki and ml for meson arch

Update the maintainers info with wiki and mailing list for the meson
platform. Fix a wrong file attribution and add maintainership for the
generic meson platforms.

Signed-off-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>