driver: clock_control: npcx: don't gate the eSPI clock if eSPI is defined

In the EC application, the system may jump between two built Zephyr
images when necessary. If we gate the eSPI clock at initialzation, it
will make the eSPI configuration which established by previous image
break and lost the communication between EC and host.

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