Update Contec Micro9 maintainer and add entry in MAINTAINERS

Cc: Ryan Mallon <ryan@bluewatersys.com>

Requires: 5744/1
Signed-off-by: Hubert Feurstein <hubert.feurstein@contec.at>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Manfred Gruber <m.gruber@tirol.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>