drm/i915/gen9: Make skl_wm_level per-plane

Having skl_wm_level contain all of the watermarks for each plane is
annoying since it prevents us from having any sort of object to
represent a single watermark level, something we take advantage of in
the next commit to cut down on all of the copy paste code in here.

Changes since v1:
- Style nitpicks
- Fix accidental usage of i vs. PLANE_CURSOR
- Split out skl_pipe_wm_active_state simplification into separate patch

Signed-off-by: Lyude <cpaul@redhat.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index e56d4a4..4d1133f 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1653,9 +1653,9 @@
 };
 
 struct skl_wm_level {
-	bool plane_en[I915_MAX_PLANES];
-	uint16_t plane_res_b[I915_MAX_PLANES];
-	uint8_t plane_res_l[I915_MAX_PLANES];
+	bool plane_en;
+	uint16_t plane_res_b;
+	uint8_t plane_res_l;
 };
 
 /*