* Cardiff back in top flight after 51-year absence * Second-placed Hull and challengers Watford lose * Bristol City defeat sees them relegated (Adds details) LONDON, April 16 (Reuters) - Cardiff City were promoted to the English Premier League on Tuesday after a 0-0 draw at home to Charlton Athletic guaranteed the Welsh side a top-two finish in the Championship (second division). Cardiff, who have agonisingly missed out in the playoffs for the last three seasons, will play in the top flight next season for the first time since 1962. ... More...