iio: imu: inv_mpu6050: Add support for MPU-6880

MPU-6880 seems to be very similar to MPU-6500 and it works
fine with some minor additions for the mpu6050 driver.

Add the necessary defines for it and make it use the same registers
as MPU-6500 but with a FIFO size of 4096.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Cc: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Link: https://lore.kernel.org/r/20201202104656.5119-2-stephan@gerhold.net


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