drm/radeon/kms: enable misc pm power state features on r5xx, rs6xx

voltage drop, dynamic voltage, dynamic sclk, pcie lane adjust, etc,

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/rs600d.h b/drivers/gpu/drm/radeon/rs600d.h
index 8f62434..a27c13a 100644
--- a/drivers/gpu/drm/radeon/rs600d.h
+++ b/drivers/gpu/drm/radeon/rs600d.h
@@ -655,6 +655,8 @@
 #define   HDP_FORCEON                                  (1 << 0)
 #define MC_HOST_DYN_CNTL                               0x1e
 #define   MC_HOST_FORCEON                              (1 << 0)
+#define DYN_BACKBIAS_CNTL                              0x29
+#define   IO_CG_BACKBIAS_EN                            (1 << 0)
 
 /* mmreg */
 #define DOUT_POWER_MANAGEMENT_CNTL                     0x7ee0