iio: backend: add support for data size set

Add backend support for setting the data size used.
This setting can be adjusted within the IP cores interfacing devices.

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/20250214131955.31973-3-antoniu.miclaus@analog.com


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