Add events for hrmp pallet. (#2532)

* Add events for hrmp pallet.

* Apply review suggestions.

polkadot/runtime/common/src/paras_registrar.rs

@@ -290,6 +290,7 @@ mod tests {
 	 		Staking: pallet_staking::{Module, Call, Config<T>, Storage, Event<T>, ValidateUnsigned},
 			Session: pallet_session::{Module, Call, Storage, Event, Config<T>},
 			Initializer: initializer::{Module, Call, Storage},
+			Hrmp: hrmp::{Module, Call, Storage, Event},
 		}
 	);
 
@@ -448,6 +449,7 @@ mod tests {
 	}
 
 	impl hrmp::Config for Test {
+		type Event = Event;
 		type Origin = Origin;
 		type Currency = pallet_balances::Module<Test>;
 	}