linux/timex.h: cleanup for userspace

Impact: fix user-space exported use

Move all the kernel-specific defines and includes into the __KERNEL__
section so that they don't get leaked into userspace.

[akpm@linux-foundation.org: coding-style fixes]

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>