dts: npcx: add device-tree files of npcx9 series.

Add device-tree files for npcx9 series such as npcx7m3f and npcx7m6f in
the following folder chart.

dts/arm/nuvoton
    |--npcx
    |    |--npcx7
    |    |    |--npcx7-miwus-wui-map.dtsi
    |    |    |--npcx7-alts-map.dtsi
    |    |    |--.....
    |    +--npcx9
    |    |    |--npcx9-miwus-wui-map.dtsi
    |    |    |--npcx9-alts-map.dtsi
    |    |    +--.....
    |    |--npcx-miwus-wui-map.dtsi
    |    |--npcx-alts-map.dtsi
    |    |--.....
    |
    |--npcx.dtsi
    |--npcx7.dtsi
    +--npcx9.dtsi

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