dt-bindings: mfd: wlf,arizona: Add spi-max-frequency

The Wolfson Microelectronics Arizona audio can be connected via SPI bus
(e.g. WM5110 on Exynos5433 TM2 board), so allow SPI peripheral
properties.

Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220504084304.46173-1-krzysztof.kozlowski@linaro.org