iio: common: st_sensors: move st_sensors_of_i2c_probe() in common code

Move st_sensors_of_i2c_probe() in st_sensors_core and rename it in
st_sensors_of_name_probe(). That change is necessary to add device-tree
support in spi code otherwise the rest of the autodetection will fail
since spi->modalias (and indio_dev->name) will be set using compatible
string value that differs from standard sensor name

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>