Since _dl_x86_cpu_features is always available, we can use x86-64
cacheinfo.c and sysconf.c for both i386 and x86-64.
* sysdeps/i386/i686/Makefile
[$(subdir) == string] (sysdep_routines): Moved to ...
* sysdeps/i386/Makefile: Here.
* sysdeps/i386/i686/cacheinfo.c: Moved to ...
* sysdeps/i386/cacheinfo.c: Here.
* sysdeps/unix/sysv/linux/i386/sysconf.c: Removed.
* sysdeps/unix/sysv/linux/i386/i686/sysconf.c: Likewise.
* sysdeps/unix/sysv/linux/x86_64/sysconf.c: Moved to ...
* sysdeps/unix/sysv/linux/x86/sysconf.c: Here.