arm: lib: import muldi3.S from Linux

Import muldi3.S from Linux 4.4.6 , commit 0d1912303e54ed1b2a371be0bba51c384dd57326
on arm32. This file implements __aeabi_lmul and it's alias __muldi3, which
is needed when doing Thumb1 builds.

This patch also defines CONFIG_THUMB2_KERNEL and CONFIG_ARM_ASM_UNIFIED
which is necessary for correct build of these files both in ARM and
Thumb mode, just like Linux does.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Tom Rini <trini@konsulko.com>