iio: adc: ltc2309: add support for ltc2305

iio: adc: ltc2309: add support for ltc2305

Add support for the LTC2305 ADC to the LTC2309 driver. The LTC2305 is
a 2-channel, 12-bit SAR ADC that is register-compatible with the
LTC2309 but has a different channel selection mapping and count.

To support multiple chips in this family, introduce ltc2309_chip_info
struct to store chip-specific channel specifications and names.
The probe function now uses i2c_get_match_data() to retrieve the
correct configuration for the detected device.

Specific channel addresses for LTC2305 (CH0, CH1, and differential
pairs) are added based on the datasheet.

Signed-off-by: Kyle Hsieh <kylehsieh1995@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>