hwmon: (lm92) Update documentation

Update datasheet references. Replace misleading 'force parameter needed'
with 'must be instantiated explicitly'. Explain the reason for the missing
auto-detection. Mention all supported chips in Kconfig.

Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>