dt-rust: Add the nrf51 flash controller

This allows a build on the nrf51, preventing an error when the
partitions are detected, but the controller wasn't.

Signed-off-by: David Brown <david.brown@linaro.org>

Author: d3zd3z

dt-rust.yaml

@@ -42,6 +42,7 @@
     value:
       names:
       - "nordic,nrf52-flash-controller"
+      - "nordic,nrf51-flash-controller"
       - "raspberrypi,pico-flash-controller"
       level: 0
   actions: