iio: accel: adxl345: Pass function pointer to core

iio: accel: adxl345: Pass function pointer to core

Provide a way for bus specific pre-configuration by adding a function
pointer argument to the driver core's probe() function, and keep
the driver core implementation bus independent.

In case NULL was passed, a regmap_write() shall initialize all bits of
the data_format register, else regmap_update() is used. In this way
spi and i2c are covered.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Link: https://lore.kernel.org/r/20240401194906.56810-6-l.rubusch@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>