iio: accel: adxl345: Add spi-3wire option

Add a setup function implementation to the spi module to enable spi-3wire
when specified in the device-tree. If spi-3wire is not specified in the
device-tree, NULL is returned as bus pre-initialization. This behavior
is identical to the i2c initialization, hence the default initialization.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Link: https://lore.kernel.org/r/20240401194906.56810-9-l.rubusch@gmail.com


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