platform/x86: apple-gmux: Move port defines to apple-gmux.h

platform/x86: apple-gmux: Move port defines to apple-gmux.h

This is a preparation patch for adding a new static inline
apple_gmux_detect() helper which actually checks a supported
gmux is present, rather then only checking an ACPI device with
the HID is there as apple_gmux_present() does.

Fixes: 21245df307cb ("ACPI: video: Add Apple GMUX brightness control detection")
Link: https://lore.kernel.org/platform-driver-x86/20230123113750.462144-1-hdegoede@redhat.com/
Reported-by: Emmanouil Kouroupakis <kartebi@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230124105754.62167-2-hdegoede@redhat.com