Since d5d332d3, a couple of links in scripts/dtc/include-prefixes
are additionally required in order to build device trees with the header
package.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>