perf bench mem: Sync memcpy assembly sources with the kernel

Commit 9a6fb28a

 ("x86/mce: Improve memcpy_mcsafe()") renames
memcpy_mcsafe() to memcpy_mcsafe_unrolled(), making
tools/arch/x86/lib/memcpy_64.S drift from the its kernel counterpart,
triggering this warning in the perf build:

  Warning: tools/arch/x86/lib/memcpy_64.S differs from kernel

Sync that copy to acknowledge that, no changes to 'perf bench' are
needed, as this function is not used there.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-xfwc1raw8obyrctxerwt1bbb@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>