[U-Boot] MAINTAINERS sorting order

[Reinhard Meyer]

Hello Wolfgang,

just as I was checking who was maintainer for at91rm9200ek, I noticed
that under the respective architecture sections there are sometimes
boards that belong to another architecture. Even my new patch for top9000
would put that line into the PPC section. Heiko e.g. has an ARM board there
as well. But there are also PPC boards in the ARM section.

I think a strict adherence to that sectionalism would in some cases
cause the same maintainer to appear multiple times. How is the preferred
way? Maybe in the future drop that sectionalism altogether?

Best Regards,
Reinhard