docs: hwmon: Document PECI drivers

docs: hwmon: Document PECI drivers

Add documentation for peci-cputemp driver that provides DTS thermal
readings for CPU packages and CPU cores, and peci-dimmtemp driver that
provides Temperature Sensor on DIMM readings.

Co-developed-by: Iwona Winiarska <iwona.winiarska@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Signed-off-by: Iwona Winiarska <iwona.winiarska@intel.com>
Link: https://lore.kernel.org/r/20220208153639.255278-13-iwona.winiarska@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>