iio: backend: add API for interface get

Add backend support for obtaining the interface type used.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Link: https://patch.msgid.link/20250214131955.31973-2-antoniu.miclaus@analog.com


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