dt-bindings: iio: gyro: adxrs290: Add interrupts support

Include 'interrupts' property and provide a suitable example for using
a GPIO interrupt line.

Signed-off-by: Nishant Malpani <nish.malpani25@gmail.com>
Link: https://lore.kernel.org/r/20200910180450.29696-3-nish.malpani25@gmail.com


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