hwmon: (sch5627) Use regmap for pwm map register caching

hwmon: (sch5627) Use regmap for pwm map register caching

Accessing virtual registers is very inefficient, so pwm map values
should be cached when possible, else userspace could effectively do
a DOS attack by reading pwm map values in a while loop.
Use the regmap cache to cache those values.

Tested on a Fujitsu Esprimo P720.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20230907052639.16491-4-W_Armin@gmx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>