zephyr: look for board-specific configuration
zephyr: look for board-specific configuration

To build Zephyr as a bootloader will typically require
overriding the default flash regions where the binary lives,
and possibly other board-specific configuration directives.
Look for boot/zephyr/targets/$(BOARD).conf and include it
in the kernel configuration if it exists.

Signed-off-by: Andrew Boie <aab045b28152628be6af0e556050d0381fd0a34d@intel.com>

ATmobica/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,tamban01/mcuboot,tamban01/mcuboot,utzig/mcuboot,utzig/mcuboot,ATmobica/mcuboot,utzig/mcuboot,tamban01/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,utzig/mcuboot,tamban01/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,utzig/mcuboot