Added memcpy/memmove family optimized with AVX512 for KNL hardware.

Added AVX512 implementations of memcpy, mempcpy, memmove, memcpy_chk,
mempcpy_chk, memmove_chk.
It shows average improvement more than 30% over AVX versions on KNL
hardware (performance results in the thread
<https://sourceware.org/ml/libc-alpha/2016-01/msg00258.html>).

    * sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Added new files.
    * sysdeps/x86_64/multiarch/ifunc-impl-list.c: Added new tests.
    * sysdeps/x86_64/multiarch/memcpy-avx512-no-vzeroupper.S: New file.
    * sysdeps/x86_64/multiarch/mempcpy-avx512-no-vzeroupper.S: Likewise.
    * sysdeps/x86_64/multiarch/memmove-avx512-no-vzeroupper.S: Likewise.
    * sysdeps/x86_64/multiarch/memcpy.S: Added new IFUNC branch.
    * sysdeps/x86_64/multiarch/memcpy_chk.S: Likewise.
    * sysdeps/x86_64/multiarch/memmove.c: Likewise.
    * sysdeps/x86_64/multiarch/memmove_chk.c: Likewise.
    * sysdeps/x86_64/multiarch/mempcpy.S: Likewise.
    * sysdeps/x86_64/multiarch/mempcpy_chk.S: Likewise.