Update codegen to use single channel in sys prop

Update sys prop name from persist.device_config.<namespace>.<flag> to persist.aconfig_flags.aconfig_flags.<namespace>.<flag>

Bug: b/295379636
Change-Id: I78f00daa574dc016902dce4b9b4ec961f973693c
diff --git a/tools/aconfig/templates/cpp_source_file.template b/tools/aconfig/templates/cpp_source_file.template
index 289e299..f373bc6 100644
--- a/tools/aconfig/templates/cpp_source_file.template
+++ b/tools/aconfig/templates/cpp_source_file.template
@@ -23,7 +23,7 @@
             } else \{
               {{ if item.readwrite- }}
               return server_configurable_flags::GetServerConfigurableFlag(
-                  "{item.device_config_namespace}",
+                  "aconfig_flags.{item.device_config_namespace}",
                   "{item.device_config_flag}",
                   "{item.default_value}") == "true";
               {{ -else- }}
@@ -50,7 +50,7 @@
         virtual bool {item.flag_name}() override \{
             {{ if item.readwrite- }}
             return server_configurable_flags::GetServerConfigurableFlag(
-                "{item.device_config_namespace}",
+                "aconfig_flags.{item.device_config_namespace}",
                 "{item.device_config_flag}",
                 "{item.default_value}") == "true";
             {{ -else- }}