platform/x86: oxpec: Move pwm_enable read to its own function

platform/x86: oxpec: Move pwm_enable read to its own function

Currently, this driver breaks 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, begin by moving the current pwm_enable read to its own
function, oxp_pwm_enable.

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/20250425111821.88746-9-lkml@antheas.dev
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>