MAINTAINERS: repair a malformed T: entry in IDMAPPED MOUNTS

The T: entries shall be composed of a SCM tree type (git, hg, quilt, stgit
or topgit) and location.

Add the SCM tree type to the T: entry and reorder the file entries in
alphabetical order.

Fixes: ddc84c90

 ("MAINTAINERS: update idmapping tree")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>