arm: kirkwood: openrd: Mark openrd boards as maintained again

arm: kirkwood: openrd: Mark openrd boards as maintained again

With the latest size increase of the openrd boards, they all compile
clean again. Let's mark them as maintained again and add the Travis
job.

Please note that I can only compile-test these targets as I don't
have access to one of those boards.

Signed-off-by: Stefan Roese <[email protected]>
Cc: Albert ARIBAUD <[email protected]>
Cc: Vagrant Cascadian <[email protected]>
Cc: Chris Packham <[email protected]>
Cc: Tom Rini <[email protected]>