small speedup.

Paravirt replacements were added to the i386 module loader by commit
139ec7c4.  This adds the same code to
the x86_64 module loader.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Acked-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>