x86/MSR: Move native_* variants to msr.h

... where they belong.

No functional change.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Cc: kvm@vger.kernel.org
Link: https://lkml.kernel.org/r/20180301151336.12948-1-bp@alien8.de