dt-bindings: iio: filter: Add lpf/hpf freq margins

Adds two properties to add a margin when automatically finding the
corner frequencies.

Signed-off-by: Sam Winchenbach <swinchenbach@arka.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250328174831.227202-2-sam.winchenbach@framepointer.org


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