iio: adc: ti-ads1015: Convert to OF match data

Replace chip type enumeration in match data with pointer to static constant
structure which contains all the different chip properties in one place, and
then replace handling of chip type in probe() with simple copy of fields in
the new match data structure into struct iio_dev.

This reduces code and increases static data.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Cc: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20220328194725.149150-8-marex@denx.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>