drivers: clock_control: npcx: Convert to use DEVICE_DT_INST_DEFINE

The NPCX clock driver was already using devicetree, just need to make a
small tweak to use DEVICE_DT_INST_DEFINE and update NPCX_CLK_CTRL_NAME
to match the label for the "nuvoton,npcx-pcc" clock controller.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>