driver: ps2: npcx: use the device Kconfig symbol

The npcx ps2 driver does not use the DT_HAS_<compat>_ENABLED Kconfig
symbol to enable the driver. This commits update the Kconig file to
use it and also drop the dependency on ESPI_PERIPHERAL_8042_KBC.

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