[REFACTOR] DynamicPartitionControl: combine DAP feature flag APIs

Combine IsDynamicPartitionsEnabled/Retrofit into one API that
returns a FeatureFlag struct instead.

This allows us to add new feature flags more easily.

Test: unittest
Change-Id: I32f0f0c4d5c636d2eac3bf99d6f92fcc6b71c7a9
diff --git a/dynamic_partition_control_android.h b/dynamic_partition_control_android.h
index e0859ed..73d7539 100644
--- a/dynamic_partition_control_android.h
+++ b/dynamic_partition_control_android.h
@@ -29,8 +29,7 @@
  public:
   DynamicPartitionControlAndroid() = default;
   ~DynamicPartitionControlAndroid();
-  bool IsDynamicPartitionsEnabled() override;
-  bool IsDynamicPartitionsRetrofit() override;
+  FeatureFlag GetDynamicPartitionsFeatureFlag() override;
   bool MapPartitionOnDeviceMapper(const std::string& super_device,
                                   const std::string& target_partition_name,
                                   uint32_t slot,