dt-bindings: adis16475: Add 'spi-cs-inactive-delay-ns' property

The devices supported by adis16475 driver require a stall period
between SPI transactions (during which the chip select is
inactive), with a minimum value equal to 16 microseconds, thus
adding 'spi-cs-inactive-delay-ns' property, which should indicate
the stall time between consecutive SPI transactions.
The specified minimum time may not be sufficient for all
configurations.
Signed-off-by: Ramona Gradinariu <ramona.gradinariu@analog.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231027140358.328699-3-ramona.gradinariu@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/imu/adi,adis16475.yaml

@@ -47,6 +47,10 @@ properties:
   spi-max-frequency:
     maximum: 2000000
 
+  spi-cs-inactive-delay-ns:
+    minimum: 16000
+    default: 16000
+
   interrupts:
     maxItems: 1