staging: iio: resolver: ad2s1210: add register/fault support summary

staging: iio: resolver: ad2s1210: add register/fault support summary

The ad2s1210 driver shoe-horns the register and fault support into IIO
events. The mapping between the registers/faults and the events is not
obvious. To save users from having to read the entire driver to figure
out how to use it, add a summary of the register/fault support to the
top of the file.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231005-ad2s1210-mainline-v4-14-ec00746840fc@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>