boards: up_squared_adsp: Add flasher script
boards: up_squared_adsp: Add flasher script

Add script signing and flashing up_squared_adsp board. Can be used:

$ west flash \
<zephyr>/boards/xtensa/up_squared_adsp/tools/flash.sh

Signed-off-by: Andrei Emeltchenko <a6565233ddc88e4fb9c66c1d70743223493f2ed4@intel.com>

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