drm/radeon: add a module parameter to disable aspm

Can cause hangs when enabled in certain motherboards.
Set radeon.aspm=0 to disable aspm.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 0010817..2f08219 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -97,6 +97,7 @@
 extern int radeon_lockup_timeout;
 extern int radeon_fastfb;
 extern int radeon_dpm;
+extern int radeon_aspm;
 
 /*
  * Copy from radeon_drv.h so we don't have to include both and have conflicting