x86: fix asm-x86/msr.h for user-space export

Use __asm__ and __volatile__ in code that is exported to userspace.  Wrap
kernel functions with __KERNEL__ so they get scrubbed.

No code changed:

   text    data     bss     dec     hex    filename
   9681036 1698924 3407872 14787832 e1a4f8 vmlinux.before
   9681036 1698924 3407872 14787832 e1a4f8 vmlinux.after

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>