dt-bindings: iio: imu: mpu6050: Document invensense,mpu6880

MPU-6880 seems to be very similar to MPU-6500 / MPU-6050 and it works
fine with some minor additions for the mpu6050 driver.
Add a compatible for it to the binding documentation.

Signed-off-by: Stephan Gerhold <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Acked-by: Jean-Baptiste Maneyrol <[e-mail]>
Cc: Jean-Baptiste Maneyrol <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/imu/invensense,mpu6050.yaml

···
       - invensense,mpu6050
       - invensense,mpu6500
       - invensense,mpu6515
+      - invensense,mpu6880
       - invensense,mpu9150
       - invensense,mpu9250
       - invensense,mpu9255