scons: Add sim_object and enums arguments to SimObject().

This will explicitly declare what SimObject and Enum types need to be set
up in C++, which will make importing all the SimObject modules during
the setup phase of SCons uneccessary.

Change-Id: Id2d7603daf33b236ceaa0789e2f089f589d34e62
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49406
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/base/SConscript

@@ -28,7 +28,7 @@
 
 Import('*')
 
-SimObject('Graphics.py')
+SimObject('Graphics.py', enums=['ImageFormat'])
 GTest('amo.test', 'amo.test.cc')
 Source('atomicio.cc', add_tags='gem5 trace')
 GTest('atomicio.test', 'atomicio.test.cc', 'atomicio.cc')