drm/i915: Kill WA 0826

According to BSpec this is not needed anymore:

"This workaround is no longer needed since NV12
support is dropped for the affected projects.
"

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181031162845.12419-2-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -4823,17 +4823,6 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
 		}
 	}
 
-	/*
-	 * Display WA #826 (SKL:ALL, BXT:ALL) & #1059 (CNL:A)
-	 * disable wm level 1-7 on NV12 planes
-	 */
-	if (wp->is_planar && level >= 1 &&
-	    (IS_SKYLAKE(dev_priv) || IS_BROXTON(dev_priv) ||
-	     IS_CNL_REVID(dev_priv, CNL_REVID_A0, CNL_REVID_A0))) {
-		result->plane_en = false;
-		return 0;
-	}
-
 	/* The number of lines are ignored for the level 0 watermark. */
 	result->plane_res_b = res_blocks;
 	result->plane_res_l = res_lines;