tools/jlink.sh: Run JlinkExe with silent when debugging

The print statements from the Jlink binary offer little additional
benefit while debugging and only clutter the output. Furthermore they
interfere with the TUI layout of GDB when one of the context layouts is
used.

dist/tools/jlink/jlink.sh

@@ -219,6 +219,7 @@ do_debug() {
     # start the J-Link GDB server
     sh -c "${JLINK_SERVER} ${JLINK_SERIAL_SERVER} \
                            -nogui \
+                           -silent \
                            -device '${JLINK_DEVICE}' \
                            -speed '${JLINK_SPEED}' \
                            -if '${JLINK_IF}' \