platform/x86: oaktrail: Use backlight power constants

Replace FB_BLANK_ constants with their counterparts from the
backlight subsystem. The values are identical, so there's no
change in functionality or semantics.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240731125220.1147348-10-tzimmermann@suse.de


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>