iio: adc: ad4080: prepare driver for multi-part support

iio: adc: ad4080: prepare driver for multi-part support

Refactor the ad4080 driver to support multiple ADC variants with
different resolution bits and LVDS CNV clock count maximums.

Changes:
- Add lvds_cnv_clk_cnt_max field to chip_info structure
- Create AD4080_CHANNEL_DEFINE macro for variable resolution/storage bits
- Make LVDS CNV clock count configurable per chip variant
- Use chip_info->product_id for chip identification comparison

This prepares the infrastructure for adding support for additional
ADC parts with different specifications while maintaining backward
compatibility with existing AD4080 functionality.

Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>