staging:iio:adc:ad7280a: Use device properties to replace platform data.

Convert all the device specific info that was previously in platform data
over to generic firmware query interfaces.

dt-bindings to follow shortly.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Link: https://lore.kernel.org/r/20220206190328.333093-15-jic23@kernel.org