drm/i915: Enable display WA#1183 from its correct spot

The DMC FW specific part of display WA#1183 is supposed to be enabled
whenever enabling DC5 or DC6, so move it to the DC6 enable function
from the DC6 disable function.

I noticed this after Daniel's patch to remove the unused
skl_disable_dc6() function.

Fixes: 53421c2fe9 ("drm/i915: Apply Display WA #1183 on skl, kbl, and cfl")
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180419155109.29451-1-imre.deak@intel.com

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -641,19 +641,18 @@ void skl_enable_dc6(struct drm_i915_private *dev_priv)
 
 	DRM_DEBUG_KMS("Enabling DC6\n");
 
-	gen9_set_dc_state(dev_priv, DC_STATE_EN_UPTO_DC6);
+	/* Wa Display #1183: skl,kbl,cfl */
+	if (IS_GEN9_BC(dev_priv))
+		I915_WRITE(GEN8_CHICKEN_DCPR_1, I915_READ(GEN8_CHICKEN_DCPR_1) |
+			   SKL_SELECT_ALTERNATE_DC_EXIT);
 
+	gen9_set_dc_state(dev_priv, DC_STATE_EN_UPTO_DC6);
 }
 
 void skl_disable_dc6(struct drm_i915_private *dev_priv)
 {
 	DRM_DEBUG_KMS("Disabling DC6\n");
 
-	/* Wa Display #1183: skl,kbl,cfl */
-	if (IS_GEN9_BC(dev_priv))
-		I915_WRITE(GEN8_CHICKEN_DCPR_1, I915_READ(GEN8_CHICKEN_DCPR_1) |
-			   SKL_SELECT_ALTERNATE_DC_EXIT);
-
 	gen9_set_dc_state(dev_priv, DC_STATE_DISABLE);
 }