drivers: uart: npcx: use PM constraint for the receiving

In this commit, the driver sets the PM constraint to prevent the system
from entering the suspend state for a CONFIG_UART_CONSOLE_INPUT_EXPIRED
period when data come in. The constraint releases after the
CONFIG_UART_CONSOLE_INPUT_EXPIRED time expires, .

With this change, the PM policy doesn't have to check the timestamp
by calling npcx_power_console_is_in_use() explictly. So the related
npcx_power_console_is_in_use*() functions can be removed.

Signed-off-by: Jun Lin <CHLin56@nuvoton.com>
Signed-off-by: Wealian Liao <WHLIAO@nuvoton.com>