x86: Add sysdeps/x86/dl-lookupcfg.h

Since sysdeps/i386/dl-lookupcfg.h and sysdeps/x86_64/dl-lookupcfg.h are
identical, we can replace them with sysdeps/x86/dl-lookupcfg.h.

	* sysdeps/i386/dl-lookupcfg.h: Moved to ...
	* sysdeps/x86/dl-lookupcfg.h: Here.
	* sysdeps/x86_64/dl-lookupcfg.h: Removed.