kconfig: Adjust ordering so that defaults work as expected

At present defaults in arch-specific Kconfig files are ignored if the
top-level item comes ahead of it in include order. This means that it is
not possible to have a U-Boot default that architectures and boards can
override. This does not seem very useful.

Move the include earlier to support this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>