driver: UART: npcx: remove unnecessary guard CONFIG_UART_INTERRUPT_DRIVEN

Currently, uart_npcx_pm_policy_state_lock* functions are guarded by
CONFIG_UART_INTERRUPT_DRIVEN && CONFIG_PM. However, it is unnecessary to
guard them with CONFIG_UART_INTERRUPT_DRIVEN as the polling mode UART
driver also uses these functions.
This commit removes it and leaves those functions guarded by CONFIG_PM
only.

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