MAINTAINERS: Retire Ralf Baechle

Ralf Baechle has been inactive for years now and the linux-mips.org site
has gone down.  No replacement contact information is available.  Thomas
has been kind enough to step up as a maintainer for EDAC-CAVIUM OCTEON
and IOC3 ETHERNET DRIVER.

Update MAINTAINERS, CREDITS, and .get_maintainer.ignore accordingly.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>