iio: adc: ad7091r: Move chip init data to container struct

AD7091R designs may differ on their communication protocol and resources
required for proper setup. Extract what is design specific into a
init_info struct so the base driver can use data and callback functions
from that struct rather than checking which specific chip is connected
during device initialization.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/1aca2261e227474dc58ce26442845947bcde9b14.1703013352.git.marcelo.schmitt1@gmail.com


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