MAINTAINERS: update Cavium ThunderX drivers

MAINTAINERS: update Cavium ThunderX drivers

Remove my maintainer entries for ThunderX drivers as I'm moving on
and won't have access to ThunderX hardware anymore and add Robert.
Also remove the obsolete addresses of David Daney and Steven Hill.

Add an entry to .mailmap for my various email addresses.

Link: https://lore.kernel.org/r/20191119190436.17875-2-rrichter@marvell.com
Cc: Ganapatrao Prabhakerrao Kulkarni <gkulkarni@marvell.com>
Cc: soc@kernel.org
Signed-off-by: Jan Glauber <jglauber@marvell.com>
Signed-off-by: Robert Richter <rrichter@marvell.com>
Signed-off-by: Olof Johansson <olof@lixom.net>