Add 32-bit Silvermont-optimized string/memory functions.

Add following functions:
bcopy, memcpy, memmove, memset, bzero, memcmp, wmemcmp, strlen,
strcpy, strncpy, stpcpy, stpncpy.
Create new directories inside arch-x86 to specify architecture: atom,
silvermont and generic (non atom or silvermont architectures are treated like generic).
Due to introducing optimized versions of stpcpy and stpncpy,
c-implementations of these functions are moved from
common for architectures makefile to arm and mips specific makefiles.

Change-Id: I990f8061c3e9bca1f154119303da9e781c5d086e
Signed-off-by: Varvara Rainchik <varvara.rainchik@intel.com>
diff --git a/libc/arch-arm/arm.mk b/libc/arch-arm/arm.mk
index 2dbcb56..06b1675 100644
--- a/libc/arch-arm/arm.mk
+++ b/libc/arch-arm/arm.mk
@@ -26,6 +26,8 @@
     upstream-freebsd/lib/libc/string/wcsrchr.c \
     upstream-freebsd/lib/libc/string/wmemcmp.c \
     upstream-openbsd/lib/libc/string/bcopy.c \
+    upstream-openbsd/lib/libc/string/stpcpy.c \
+    upstream-openbsd/lib/libc/string/stpncpy.c \
     upstream-openbsd/lib/libc/string/strlcat.c \
     upstream-openbsd/lib/libc/string/strlcpy.c \
     upstream-openbsd/lib/libc/string/strncat.c \