iio: proximity: as3935: noise detection + threshold changes

Most applications are too noisy to allow the default noise and
watchdog settings, and thus need to be configurable via DT
properties.

Also default settings to POR defaults on a reset, and register
distuber interrupts as noise since it prevents proper usage.

Cc: devicetree@vger.kernel.org
Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>