refcount: change EXPORT_SYMBOL markings

Now that kref is using the refcount apis, the _GPL markings are getting
exported to places that it previously wasn't.  Now kref.h is GPLv2
licensed, so any non-GPL code using it better be talking to some
lawyers, but changing api markings isn't considered "nice", so let's fix
this up.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit d557d1b58b3546bab2c5bc2d624c5709840e6b10)