iio: dac: ltc2632: drop enum and use individual chip_info objects

iio: dac: ltc2632: drop enum and use individual chip_info objects

Remove the ltc2632_chip_info_tbl[] array and related
ltc2632_supported_device_ids enum used for looking up chip-specific
information. Instead, use separate static const struct
ltc2632_chip_info objects for each supported chip variant.

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: David Marinovic <david.marinovic@pupin.rs>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>