ARM: dts: rpi-4: disable wifi frequencies

The RPi4 WiFi chip and HDMI outputs have some frequency overlap with
crosstalk around 2.4GHz. Let's mark it as such so we can use some evasive
maneuvers.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20201029134018.1948636-3-maxime@cerno.tech