dt-bindings: arm: bcm2835: Add Raspberry Pi 400 to DT schema

Add new Raspberry Pi 400 to DT schema.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1622981777-5023-5-git-send-email-stefan.wahren@i2se.com


Signed-off-by: Nicolas Saenz Julienne <nsaenz@kernel.org>