nrf: add microbit-s110v8 target

This makes it possible to use Bluetooth on the BBC micro:bit.

Note that you need to use -programmer=cmsis-dap otherwise the SoftDevice
will be erased while flashing something that uses Bluetooth.

targets/nrf51-s110v8.json

@@ -0,0 +1,4 @@
+{
+	"build-tags": ["softdevice", "s110v8"],
+	"linkerscript": "targets/nrf51-s110v8.ld"
+}