Add a devicetree/zephyr.h header, which is meant to contain
definitions for /chosen properties specific to Zephyr.
Currently, this just deals with zephyr,entropy. We add a
DT_CHOSEN_ZEPHYR_ENTROPY_LABEL macro which expands to the label for the
node pointed to by zephyr,entropy.
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>