arm64: dts: imx8mp: Add MEDIA_BLK_CTRL

Add a DT node for the MEDIA_BLK_CTRL, which provides power domains for
the camera and display devices.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>