arm64: dts: imx8mm-kontron: Add support for display bridges on BL i.MX8MM
The Kontron Electronics BL i.MX8MM has oboard disply bridges for
DSI->HDMI and DSI->LVDS conversion. The DSI interface is muxed by
a GPIO-controlled switch to one of these two bridges.
By default the HDMI bridge is enabled. The LVDS bridge can be
selected by loading an additional (panel-specific) overlay.