docs: add missing Kconfig functions
docs: add missing Kconfig functions

Add missing Kconfig functions to documentation about Kconfig
preprocessor functions.

Signed-off-by: Michał Barnaś <77666125932addc6fc525b281b518fd8fd2203d8@semihalf.com>

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