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/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 10a0cf2..84301d3 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -468,9 +468,13 @@
 	bool sprites_scaled;
 };
 
-struct skl_pipe_wm {
+struct skl_plane_wm {
 	struct skl_wm_level wm[8];
 	struct skl_wm_level trans_wm;
+};
+
+struct skl_pipe_wm {
+	struct skl_plane_wm planes[I915_MAX_PLANES];
 	uint32_t linetime;
 };