hwmon: (gpd-fan): drop global driver data and use per-device allocation

hwmon: (gpd-fan): drop global driver data and use per-device allocation

replace the global state gpd_driver_priv with per-device private data
(struct gpd_fan_data) allocated in probe. This allows the driver to
support multiple instances in the future and aligns with kernel best
practices.

No functional change intended.

Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
Link: https://lore.kernel.org/r/1cd3e13033fdd3d0f9b59322f7c86e350d113b92.1781055639.git.xiaopei01@kylinos.cn
Signed-off-by: Guenter Roeck <linux@roeck-us.net>