kernel: improve help text of INIT_STACKS option
kernel: improve help text of INIT_STACKS option

This commit improves the help text of INIT_STACKS
Kconfig option, so it indicates that the stack
initialization applies also to the interrupt stack.

Fixes #7196.

Signed-off-by: Ioannis Glaropoulos <5921cc8bab7e1d4329f52fd8f6268f9692e3de80@nordicsemi.no>

zephyrproject-rtos/zephyr,punitvara/zephyr,Vudentz/zephyr,ldts/zephyr,nashif/zephyr,ldts/zephyr,galak/zephyr,explora26/zephyr,explora26/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,ldts/zephyr,ldts/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,finikorg/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr,punitvara/zephyr,explora26/zephyr,Vudentz/zephyr,punitvara/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,ldts/zephyr,explora26/zephyr