The spillover effect of China Evergrande Group's debt problems on the banking system is controllable, a central bank official said on Friday, in rare official comments on a liquidity crisis at the massive developer that has roiled global markets.   Chinese authorities are urging Evergrande to step up asset disposals and the resumption of projects, Zou Lan, head of financial markets at the People's Bank of China (PBoC), told a briefing, adding that individual financial institutions did not have highly concentrated exposure to Evergrande.