iio: backend: introduce struct iio_backend_info

iio: backend: introduce struct iio_backend_info

Instead of only passing the backend ops when calling
devm_iio_backend_register(), pass an info like structure that will
contains the ops and additional information. Fow now, the backend name
is being added as that will be used by the debugFS interface introduced
in a later patch.

It also opens the door for further customizations passed by backends.

All users of devm_iio_backend_register() were updated accordingly.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240802-dev-iio-backend-add-debugfs-v2-1-4cb62852f0d0@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>