kernel: Clarify timeout and sleep API regarding negative inputs
kernel: Clarify timeout and sleep API regarding negative inputs

Timeout and use s32_t as an argument but only positive values are
accepted (or special value like K_FOREVER). It was not specified in
the description which may lead to misinterpretation.

Signed-off-by: Krzysztof Chruscinski <9b6dc988558c51b0405b49b55c8e66862969844b@nordicsemi.no>

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