watchdog: w83627hf: Use helper functions to access superio registers

Use helper functions named similar to other drivers to access
superio registers.

Request memory region only when needed, and use request_muxed_region().
This lets other devices (hwmon, gpio) use the same region.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>