arm: socfpga: Add myself as maintainer for the SoCrates board

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Marek Vasut <marex@denx.de>
Acked-by: Pavel Machek <pavel@denx.de>
Cc: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Vince Bridgers <vbridger@altera.com>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>