* Lisbon&aposs PSI-20 equity index outperforms to rise 0.2 pct* Portuguese market buoyed by signs of economic recovery* Credit Suisse cuts Germany to "benchmark" vs "overweight"* Backdrop of M&A activity cushions stock marketsBy Sudip Kar-GuptaLONDON, May 6 (Reuters) - European stock markets fell across the board on Tuesday, apart from Lisbon which swam against the tide as new signs of a Portugues