iio: document inv_icm42600 driver private sysfs attributes

Add ABI documentation for inv_icm42600 private sysfs attributes.
Signed-off-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
Link: https://lore.kernel.org/r/20240605195949.766677-2-inv.git-commit@tdk.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-inv_icm42600

+What:		/sys/bus/iio/devices/iio:deviceX/in_accel_power_mode
+KernelVersion:	6.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Accelerometer power mode. Setting this attribute will set the
+		requested power mode to use if the ODR support it. If ODR
+		support only 1 mode, power mode will be enforced.
+		Reading this attribute will return the current accelerometer
+		power mode if the sensor is on, or the requested value if the
+		sensor is off. The value between real and requested value can
+		be different for ODR supporting only 1 mode.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_accel_power_mode_available
+KernelVersion:	6.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		List of available accelerometer power modes that can be set in
+		in_accel_power_mode attribute.

MAINTAINERS

@@ -11520,6 +11520,7 @@ M:	Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
 L:	linux-iio@vger.kernel.org
 S:	Maintained
 W:	https://invensense.tdk.com/
+F:	Documentation/ABI/testing/sysfs-bus-iio-inv_icm42600
 F:	Documentation/devicetree/bindings/iio/imu/invensense,icm42600.yaml
 F:	drivers/iio/imu/inv_icm42600/