dt-bindings: display: Add a property to deal with WiFi coexistence

dt-bindings: display: Add a property to deal with WiFi coexistence

The RaspberryPi4 has both a WiFi chip and HDMI outputs capable of doing
4k. Unfortunately, the 1440p resolution at 60Hz has a TMDS rate on the
HDMI cable right in the middle of the first Wifi channel.

Add a property to our HDMI controller, that could be reused by other
similar HDMI controllers, to allow the OS to take whatever measure is
necessary to avoid that crosstalk.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201029134018.1948636-1-maxime@cerno.tech