* TSX up 89.44 points, or 0.70 percent, at 12,821.83 * Eight of 10 main index sectors advance * RBC gains 0.9 percent after results * Gold miners follow bullion prices lower By John Tilak and Alastair Sharp TORONTO, Feb 28 (Reuters) - Forecast-topping quarterly results from Royal Bank of Canada and Toronto-Dominion Bank, the country's two biggest banks, helped drive Canada's main stock index higher on Thursday, overcoming weakness in gold miners. The market was also supp