iio: resolver: ad2s1210: move out of staging

This moves the ad2s1210 resolver driver out of staging. The driver has
been fixed up and is ready to graduate.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231010-ad2s1210-mainline-v5-4-35a0f6ffa04a@baylibre.com


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