tools: use print function in Python 3 code

tools: use print function in Python 3 code

This GDB script was converted to use Python 3 along with all other
Python scripts in commit b95f5528cc, but still used the Python 2 print
statement syntax instead of the Python 3 print function. Fix that.

We also add the Python 2 compatibility statement, just in case some GDB
still uses Python 2 instead of Python 3.