iio: ABI: temperature: Unify documentation for thermocouple fault detection.

Kernel documentation for a given ABI element should not be duplicated
in multiple files, so pull them into one higher level documentation file.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Navin Sankar Velliangiri <navin@linumiz.com>
Cc: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/20220626165511.602202-2-jic23@kernel.org