dt-bindings: mfd: syscon: Add microchip,lan966x-cpu-syscon compatible

Add the Microchip LAN966x CPU system registers compatible.

Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220313003122.19155-1-michael@walle.cc