iio: imu/mpu6050: support dual-edge IRQ

Make mpu6050 usable on platforms which provide only any-edge interrupts.
One example of this kind of platform is AT91SAM9G45

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>