[PATCH] hpet header sanitization

Add __KERNEL__ block.
Use __KERNEL__ to allow ioctl interface to be usable.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>