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>).