staging: iio: ad7780: generates pattern_mask from PAT bits

Previously, all pattern_masks and patterns in the chip_info table were
hardcoded. Now they are generated using the PAT macros, as described in
the datasheets.

Signed-off-by: Giuliano Belinassi <giuliano.belinassi@usp.br>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>