dev: Include the platform base class even in NULL_ISA builds.

These classes don't have any ISA specific aspects.

Change-Id: Ifefb12d23e4aee8e3fd56f0a1eb3d9ad00e733a0
Reviewed-on: https://gem5-review.googlesource.com/c/13467
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

src/dev/SConscript

@@ -39,17 +39,18 @@ Source('dma_device.cc')
 DebugFlag('IsaFake')
 DebugFlag('DMA')
 
+SimObject('Platform.py')
+Source('platform.cc')
+
 if env['TARGET_ISA'] == 'null':
     Return()
 
 SimObject('BadDevice.py')
-SimObject('Platform.py')
 
 Source('baddev.cc')
 Source('intel_8254_timer.cc')
 Source('mc146818.cc')
 Source('pixelpump.cc')
-Source('platform.cc')
 
 DebugFlag('Intel8254Timer')
 DebugFlag('MC146818')