driver: clock_control: npcx: power down some modules by default

This commit sets the power down bit of the module SDP, UART3, UART4,
and I3C by default. The module's driver should take the responsibility
to clear it to turn on the power. It helps reduce the power consumption
when an application doesn't use these modules.

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