linux/hdsmart.h: fix goofups (take 2)
Fix goofups of commit 76166952bbc81dda1c8a8c14e75a2aa06f6c052c
("<linux/hdsmart.h> is not used by kernel code").
Also update include/linux/Kbuild to reflect the fact that hdsmart.h
uses __KERNEL__ ifdefs now.
Reported-by: "Robert P. J. Day" <rpjday@crashcourse.ca>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>