cmake: define and create KCONFIG_BINARY_DIR if it doesn't exists
cmake: define and create KCONFIG_BINARY_DIR if it doesn't exists

The Zephyr CMake module kconfig.cmake will create files inside
KCONFIG_BINARY_DIR.

In a default Zephyr build setup, this directory is created by Zephyr
CMake module zephyr_module.cmake. But Zephyr CMake modules are modular
and thus it must be possible to use kconfig module without
zephyr_module.

Thus kconfig.cmake must set and create KCONFIG_BINARY_DIR if it does not
already exists.

Signed-off-by: Torsten Rasmussen <a7c5b1d5a1f41fce6edfa3f7c2392ae0c59deafe@nordicsemi.no>

galak/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr