iio: dac: ti-dac082s085: Read chip spec from device table

The two properties unique to each supported chip, resolution and number
of channels, are currently gleaned from the chip's name.
E.g. dac102s085 is a dual channel 10-bit DAC.
        ^^^
This was deemed unmaintainable by the subsystem maintainer once the
driver is extended to support further chips, hence it was requested
to add an explicit table for chip-specific information and use an
enum to reference into it.

This adds 17 LoC without any immediate gain, so make the change in a
separate commit which can be reverted if we determine in 10 years that
it was unnecessary.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>