drm_hwcomposer: Deprecate usage of HWC2 GetActiveConfig

Add HwcDisplay::GetLastRequestedConfig, and use this to implement
support for getActiveConfig.

Change-Id: I089e2ac0046eceb5da9c130537105290a973ae4a
Signed-off-by: Drew Davenport <ddavenport@google.com>
diff --git a/hwc2_device/HwcDisplay.cpp b/hwc2_device/HwcDisplay.cpp
index 0ab43f9..ec481e1 100644
--- a/hwc2_device/HwcDisplay.cpp
+++ b/hwc2_device/HwcDisplay.cpp
@@ -104,6 +104,14 @@
   return &config_iter->second;
 }
 
+const HwcDisplayConfig *HwcDisplay::GetLastRequestedConfig() const {
+  auto config_iter = configs_.hwc_configs.find(staged_mode_config_id_);
+  if (config_iter == configs_.hwc_configs.end()) {
+    return nullptr;
+  }
+  return &config_iter->second;
+}
+
 void HwcDisplay::SetPipeline(std::shared_ptr<DrmDisplayPipeline> pipeline) {
   Deinit();