Adds support for reading the critical values of the temperature sensors
and the rail sensors (voltage and current) once and caches them. Updates
the naming of the constants following a more clear scheme. Also updates
the documentation and fixes some typos. Updates is_visible and ops_read
functions to be more readable.

The new sensors output of a Corsair HX850i will look like this:
corsairpsu-hid-3-1
Adapter: HID adapter
v_in:        230.00 V
v_out +12v:   12.14 V  (crit min =  +8.41 V, crit max = +15.59 V)
v_out +5v:     5.03 V  (crit min =  +3.50 V, crit max =  +6.50 V)
v_out +3.3v:   3.30 V  (crit min =  +2.31 V, crit max =  +4.30 V)
psu fan:        0 RPM
vrm temp:     +46.2°C  (crit = +70.0°C)
case temp:    +39.8°C  (crit = +70.0°C)
power total: 152.00 W
power +12v:  108.00 W
power +5v:    41.00 W
power +3.3v:   5.00 W
curr +12v:     9.00 A  (crit max = +85.00 A)
curr +5v:      8.31 A  (crit max = +40.00 A)
curr +3.3v:    1.62 A  (crit max = +40.00 A)
Signed-off-by: Wilken Gottwalt <wilken.gottwalt@posteo.net>
Link: https://lore.kernel.org/r/YFNg6vGk3sQmyqgB@monster.powergraphx.localSigned-off-by: Guenter Roeck <linux@roeck-us.net>