The bindings are missing documentation for some of the compatible
strings.

Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>