west: fix import error on sign.py
west: fix import error on sign.py

Fix broken imports caused by changes
from its dependencies.

Signed-off-by: Jun Li <3d873abd46e48a508cfeae575fcd9ffe09e1a769@intel.com>

ldts/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,ldts/zephyr,Vudentz/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,ldts/zephyr,finikorg/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr