cmake: Add sorting of linker snippets by key
cmake: Add sorting of linker snippets by key

Allows snippets to be placed in a predictable order into the linker
script. This is useful for data that must be placed at a particular
location.

Signed-off-by: Øyvind Rønningstad <5f9e1eedbdafebd99226f1498f634e1047455d88@nordicsemi.no>

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