hwmon: (jc42) Convert register access and caching to regmap/regcache

Switch the jc42 driver to use an I2C regmap to access the registers.
Also move over to regmap's built-in caching instead of adding a
custom caching implementation. This works for JC42_REG_TEMP_UPPER,
JC42_REG_TEMP_LOWER and JC42_REG_TEMP_CRITICAL as these values never
change except when explicitly written. The cache For JC42_REG_TEMP is
dropped (regmap can't cache it because it's volatile, meaning it can
change at any time) as well for simplicity and consistency with other
drivers.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20221023213157.11078-2-martin.blumenstingl@googlemail.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/Kconfig

@@ -807,6 +807,7 @@ config SENSORS_IT87
 config SENSORS_JC42
 	tristate "JEDEC JC42.4 compliant memory module temperature sensors"
 	depends on I2C
+	select REGMAP_I2C
 	help
 	  If you say yes here, you get support for JEDEC JC42.4 compliant
 	  temperature sensors, which are used on many DDR3 memory modules for