doc: cmake: refactor kconfig
doc: cmake: refactor kconfig

Refactor the Kconfig target. Mostly formatting in this case. The Kconfig
script is also added as a dependency of the CMake configuration step, so
that if it is changed, the Kconfig generation step will be re-run.

Signed-off-by: Gerard Marull-Paretas <bedb45f43a286e49f4dcda039a436b216ae61ef3@nordicsemi.no>

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