iio:imu:mpu6050 update i2c bindings to reflect i2c-gate and supported parts

These bindings are somewhat lagging the state of the driver.  The i2c-gate
bindings are documented elsewhere, but it seems sensible to at least have
an example and cross reference in here.  SPI bindings will need to be the
subject of a future patch.
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/iio/imu/inv_mpu6050.txt

@@ -3,14 +3,20 @@ InvenSense MPU-6050 Six-Axis (Gyro + Accelerometer) MEMS MotionTracking Device
 http://www.invensense.com/mems/gyro/mpu6050.html
 
 Required properties:
- - compatible : should be "invensense,mpu6050"
+ - compatible : should be one of
+		"invensense,mpu6050"
+ 		"invensense,mpu6500"
+		"invensense,mpu9150"
+		"invensense,icm20608"
  - reg : the I2C address of the sensor
  - interrupt-parent : should be the phandle for the interrupt controller
  - interrupts : interrupt mapping for GPIO IRQ
 
 Optional properties:
  - mount-matrix: an optional 3x3 mounting rotation matrix
-
+ - i2c-gate node.  These devices also support an auxiliary i2c bus.  This is
+   simple enough to be described using the i2c-gate binding. See
+   i2c/i2c-gate.txt for more details.
 
 Example:
 	mpu6050@68 {
@@ -28,3 +34,19 @@ Example:
 		               "0",                   /* y2 */
 		               "0.984807753012208";   /* z2 */
 	};
+
+
+	mpu9250@68 {
+		compatible = "invensense,mpu9250";
+		reg = <0x68>;
+		interrupt-parent = <&gpio3>;
+		interrupts = <21 1>;
+		i2c-gate {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			ax8975@c {
+				compatible = "ak,ak8975";
+				reg = <0x0c>;
+			};
+		};
+	};