x86: Make alternative instruction pointers relative

This save a few bytes on x86-64 and means that future patches can
apply alternatives to unrelocated code.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Link: http://lkml.kernel.org/r/ff64a6b9a1a3860ca4a7b8b6dc7b4754f9491cd7.1310563276.git.luto@mit.edu


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>