By Francesco Guarascio and Robin Emmott BRUSSELS (Reuters) - Turkey will help stem the flow of migrants to Europe in return for cash, visas and renewed talks on joining the EU in a deal struck on Sunday that the Turkish prime minister called a "new beginning" for the uneasy neighbours. Leaders of the 28 European Union states met Turkish premier Ahmet Davutoglu in Brussels on Sunday evening to give their collective political blessing to an agreement hammered out by diplomats over the past few weeks. A key element is 3 billion euros ($3.2 billion) in EU aid for the 2.2 million Syrian refugees in Turkey, intended to raise living standards and so persuade more to stay put rather than attempt often perilous crossings to the Greek islands and the EU.