drm_hwcomposer: Stop using HWC2 for layer z order

Add z_order to LayerProperties and set it along with other properties

Change-Id: Ib98c653e0adbc8da0ef50d64bd734b9014b09caa
Signed-off-by: Drew Davenport <ddavenport@google.com>
diff --git a/hwc2_device/HwcLayer.cpp b/hwc2_device/HwcLayer.cpp
index ded8acd..cd2a319 100644
--- a/hwc2_device/HwcLayer.cpp
+++ b/hwc2_device/HwcLayer.cpp
@@ -50,6 +50,9 @@
   if (layer_properties.transform) {
     layer_data_.pi.transform = layer_properties.transform.value();
   }
+  if (layer_properties.z_order) {
+    z_order_ = layer_properties.z_order.value();
+  }
 }
 
 // NOLINTNEXTLINE(readability-convert-member-functions-to-static)