platform/x86: oxpec: Move pwm value read/write to separate functions

platform/x86: oxpec: Move pwm value read/write to separate functions

Currently, this driver breaks hwmon ABI by using auto as 0 and manual
as 1. However, for pwm_enable, 0 is full speed, 1 is manual, and 2 is
auto. For the correction to be possible, this means that the pwm_enable
endpoint will need access to both pwm enable and value (as for the 0th
value, the fan needs to be set to full power).

Therefore, move the pwm value read/write to separate functions.

Reviewed-by: Derek J. Clark <derekjohn.clark@gmail.com>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
Link: https://lore.kernel.org/r/20250425111821.88746-10-lkml@antheas.dev
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>