MAINTAINERS: Add entry for megachips-stdpxxxx-ge-b850v3-fw

Add MAINTAINERS entry for the second video output of the GE B850v3:
       STDP4028-ge-b850v3-fw bridges (LVDS-DP)
       STDP2690-ge-b850v3-fw bridges (DP-DP++)

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Martyn Welch <martyn.welch@collabora.co.uk>
Cc: Martin Donnelly <martin.donnelly@ge.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
CC: David Airlie <airlied@linux.ie>
CC: Thierry Reding <treding@nvidia.com>
CC: Thierry Reding <thierry.reding@gmail.com>
CC: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Peter Senna Tschudin <peter.senna@collabora.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/a62877dcaee004d82809fe77b6d154b65f466729.1488555615.git.peter.senna@collabora.com