drm/radeon/kms: dynclks fixes

- only r4xx/r5xx/rs6xx/rs740 have clock gating atom table,
so disable it on r6xx.  it's already disabled on r7xx
- check to make sure the clock_gating hook exists before
calling it.  This avoids a segfault on asics without
that function.
- remove unused static power management function.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon_clocks.c b/drivers/gpu/drm/radeon/radeon_clocks.c
index 73c4405..3ec94a0 100644
--- a/drivers/gpu/drm/radeon/radeon_clocks.c
+++ b/drivers/gpu/drm/radeon/radeon_clocks.c
@@ -846,8 +846,10 @@
 	/* XXX make sure engine is idle */
 
 	if (radeon_dynclks != -1) {
-		if (radeon_dynclks)
-			radeon_set_clock_gating(rdev, 1);
+		if (radeon_dynclks) {
+			if (rdev->asic->set_clock_gating)
+				radeon_set_clock_gating(rdev, 1);
+		}
 	}
 	radeon_apply_clock_quirks(rdev);
 	return 0;