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/evergreen.c b/drivers/gpu/drm/radeon/evergreen.c
index 526e428..038dcac 100644
--- a/drivers/gpu/drm/radeon/evergreen.c
+++ b/drivers/gpu/drm/radeon/evergreen.c
@@ -5515,6 +5515,9 @@
 	 */
 	bool fusion_platform = false;
 
+	if (radeon_aspm == 0)
+		return;
+
 	if (!(rdev->flags & RADEON_IS_PCIE))
 		return;