x86-64: Reduce SMP locks table size

Reduce the SMP locks table size by using relative pointers instead of
absolute ones, thus cutting the table size by half.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <4BCF30FE020000780003B3B6@vpn.id2.novell.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>