iio: inkern: move to fwnode properties

iio: inkern: move to fwnode properties

This moves the IIO in kernel interface to use fwnode properties and thus
be firmware agnostic.

Note that the interface is still not firmware agnostic. At this point we
have both OF and fwnode interfaces so that we don't break any user. On
top of this we also want to have a per driver conversion and that is the
main reason we have both of_xlate() and fwnode_xlate() support.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220715122903.332535-6-nuno.sa@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>