iio: adc: ad7606: move scale_setup as function pointer on chip-info

iio: adc: ad7606: move scale_setup as function pointer on chip-info

Up until now, all ADCs were 16-bit precision.
With the addition of the AD7606C some things will change. For one thing,
we'll need to setup available-scales for each channel. Also for the 18-bit
precision variants, the scales will be different.

This change adds a function-pointer to the chip-info struct to be able to
set this up (differently) for the new parts. For the current parts, the
scales are the same (for all parts) between HW and SW modes.

Also creating a 'ad7606_sw_mode_setup()' function that must be called
before the scale_setup callback. This is needed in case SW mode is enabled
for some ADCs.

Signed-off-by: Alexandru Ardelean <aardelean@baylibre.com>
Link: https://patch.msgid.link/20240919130444.2100447-4-aardelean@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>