* CEO bullish on data; 90 pct of Bahraini broadband is over mobile * Viva annual revenue rose 21 pct in 2013, outstripping rivals * Firm seeks to counter fall in conventional calls, texts By Matt Smith DUBAI, Sept 29 (Reuters) - Viva Bahrain, the country's **.2 telecom operator by income, expects data to account for at least half of revenue within two years - from a quarter **w - as it seeks to counter a decline in conventional calls and texts, its chief executive told Reuters. ...