cmake: dts: Remove duplicates from DTS_ROOT
cmake: dts: Remove duplicates from DTS_ROOT

If duplicates gets passed to scripts/dts/gen_defines.py, the bindings in
those directories will be loaded twice and actually get in conflict with
itself.

Signed-off-by: Tobias Svehagen <d3302b125bdd383498bbe4afb41749ba75a64b52@gmail.com>

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