Kill unneeded #include <linux/kconfig.h>

Because the top-level Makefile forces all the source files
to include include/linux/kconfig.h (see the UBOOTINCLUDE define),
these includes are redundant.

By the way, there are exceptions for the statement above; host
programs.  In fact, host tools in U-Boot depend on a particular
board configuration, although I think they should not.  So, some
files still include <linux/config.h> to work around build errors
on host tools.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Acked-by: Simon Glass <sjg@chromium.org>