hwmon: (f75375s) Initialize pwmX_mode and pwmX_enable if there is no platform data

pwmX_mode and pwmX_enable are not initialized if no platform data is provided to
the driver. Read chip configuration at driver initialization time and initialize
attributes to reflect chip configuration.

Cc: Riku Voipio <riku.voipio@iki.fi>
Reviewed-by: Bjoern Gerhart <oss@extracloud.de>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>