drm/bridge: imx8mp-hdmi-tx-connector-fixup: show a warning when adding the overlay

drm/bridge: imx8mp-hdmi-tx-connector-fixup: show a warning when adding the overlay

Describing the HDMI connector in device tree is recommended. While the
overlay insertion is a workaround to avoid breaking existing devices, every
dts should be improved by adding a connector description.

Add a warning to make users aware as far as possible.

As a warning line cannot hold all the relevant info, add a detailed comment
in the code so it easy to find when the warning is seen.

Reviewed-by: Liu Ying <victor.liu@nxp.com>
Link: https://patch.msgid.link/20260407-drm-lcdif-dbanc-v4-9-247a16e61ef9@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>