swig: Fix issue with circular import in 2.0.9/2.0.10

This patch fixes an issue which prevented gem5 from running when built
using swig 2.0.9 and 2.0.10. The generated event.py tried to import
m5.internal which in turn relied on importing event. This patch seems
to fix the problem, and so far has not caused any other issues.

src/python/m5/__init__.py

@@ -32,7 +32,7 @@
 
 try:
     # Try to import something that's generated by swig
-    import internal
+    import internal.core
 
     # Try to grab something from it in case demandimport is being used
     internal.core.curTick

src/python/m5/internal/__init__.py

@@ -25,10 +25,3 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #
 # Authors: Nathan Binkert
-
-import core
-import debug
-import event
-import stats
-import trace
-from drain import DrainManager, Drainable