dt-bindings: bmi160 document open-drain property

We have added an optional boolean property for configuring a BMI160
interrupt pin as open-drain, as opposed to the default push-pull, so
document this.
Signed-off-by: Martin Kelly <martin@martingkelly.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/imu/bmi160.txt

@@ -12,6 +12,8 @@ Optional properties:
  - interrupts : interrupt mapping for IRQ
  - interrupt-names : set to "INT1" if INT1 pin should be used as interrupt
    input, set to "INT2" if INT2 pin should be used instead
+ - drive-open-drain : set if the specified interrupt pin should be configured as
+   open drain. If not set, defaults to push-pull.
 
 Examples: