iio: imu: inv_icm42600: add core of new inv_icm42600 driver

Core component of a new driver for InvenSense ICM-426xx devices.
It includes registers definition, main probe/setup, and device
utility functions.

ICM-426xx devices are latest generation of 6-axis IMU,
gyroscope+accelerometer and temperature sensor. This device
includes a 2K FIFO, supports I2C/I3C/SPI, and provides
intelligent motion features like pedometer, tilt detection,
and tap detection.
Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>