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

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.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>