Allow initializing fans on systems where BIOS does not do that by
default.

 - define f75375s_platform_data in new file f75375s.h
 - if platform_data was provided, set fans accordingly in f75375_init()
 - split set_pwm_enable() to a sysfs callback and directly usable
   set_pwm_enable_direct()
Signed-off-by: Riku Voipio <riku.voipio@movial.fi>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>