Move sysdeps/x86_64/multiarch/init-arch.h to sysdeps/x86/init-arch.h
which can be used for both i386 and x86_64.
* sysdeps/i386/i686/multiarch/init-arch.h: Removed.
* sysdeps/unix/sysv/linux/x86/init-arch.h: Likewise.
* sysdeps/x86_64/cacheinfo.c: Include <init-arch.h> instead
of "multiarch/init-arch.h".
* sysdeps/x86_64/multiarch/init-arch.h: Renamed to ...
* sysdeps/x86/init-arch.h: This.
