pgl: Implement pgl::srv::Initialize

libraries/libstratosphere/include/stratosphere/pm/pm_shell_api.hpp

@@ -27,5 +27,6 @@ namespace ams::pm::shell {
     Result TerminateProcess(os::ProcessId process_id);
     Result GetApplicationProcessIdForShell(os::ProcessId *out);
     Result BoostSystemMemoryResourceLimit(u64 size);
+    Result EnableApplicationExtraThread();
 
 }