config: Add a --without-python option to build process

Add the ability to build libgem5 without embedded Python or the
ability to configure with Python.

This is a prelude to a patch to allow config.ini files to be loaded
into libgem5 using only C++ which would make embedding gem5 within
other simulation systems easier.

This adds a few registration interfaces to things which cross
between Python and C++.  Namely: stats dumping and SimObject resolving

src/sim/debug.hh

@@ -53,8 +53,6 @@ void takeCheckpoint(Tick when);
  */
 void eventqDump();
 
-void py_interact();
-
 int getRemoteGDBPort();
 // Remote gdb base port.  0 disables remote gdb.
 void setRemoteGDBPort(int port);