MAINTAINERS: Add IPUv3 core driver to the i.MX DRM driver section

The ipu-v3 core driver is maintained in and merged through
the same trees as the imx-drm drivers that are using it.
This patch adds the drivers/gpu/ipu-v3/ directory to the
i.MX DRM driver section.
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

MAINTAINERS

@@ -3617,6 +3617,7 @@ M:	Philipp Zabel <p.zabel@pengutronix.de>
 L:	dri-devel@lists.freedesktop.org
 S:	Maintained
 F:	drivers/gpu/drm/imx/
+F:	drivers/gpu/ipu-v3/
 F:	Documentation/devicetree/bindings/drm/imx/
 
 DRM DRIVERS FOR NVIDIA TEGRA