add ARINC653 scheduler maintainers

add ARINC653 scheduler maintainers

Previously the ARINC653 scheduler was indirectly maintained by
Kathy Hadley and Josh Holtrop being cc'd on changes by George
Dunlap.  Maintenance is currently being done by Robert VanVossen
and myself.  To avoid potential communication problems in the
future, make Robbie and I the official maintainers.

Signed-off-by:  Nathan Studer <nate.studer@dornerworks.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>