binman: Allow configuration options to be used in .dts files

It is sometimes useful to be able to reference configuration options in a
device tree source file. Add the necessary includes so that this works.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>