x86: kmsan: use C versions of memset16/memset32/memset64

KMSAN must see as many memory accesses as possible to prevent false
positive reports.  Fall back to versions of
memset16()/memset32()/memset64() implemented in lib/string.c instead of
those written in assembly.

Link: https://lkml.kernel.org/r/20230303141433.3422671-3-glider@google.com


Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>