[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/mock_dynamic_partition_control.h b/mock_dynamic_partition_control.h
index 310e528..a0701e7 100644
--- a/mock_dynamic_partition_control.h
+++ b/mock_dynamic_partition_control.h
@@ -49,8 +49,7 @@
                     android::fs_mgr::MetadataBuilder*,
                     uint32_t));
   MOCK_METHOD1(GetDeviceDir, bool(std::string*));
-  MOCK_METHOD0(IsDynamicPartitionsEnabled, bool());
-  MOCK_METHOD0(IsDynamicPartitionsRetrofit, bool());
+  MOCK_METHOD0(GetDynamicPartitionsFeatureFlag, FeatureFlag());
 };
 
 }  // namespace chromeos_update_engine