iio: st_sensors: Make accel, gyro, magn and pressure probe shared

Some IMUs may utilize existing library code for STMicro accelerometer,
gyroscope, magnetometer and pressure. Let's share them via st_sensors.h.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210414195454.84183-5-andriy.shevchenko@linux.intel.com


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