Modify the default example design generated by the CORE Generator in the ISE Design Suite 13.2 as follows to make sure that the GTRXRESET pin asserts until the PLL locks.
In *_block.vhd file:Replace:
mgt_rx_reset <= reset 156 or (not mgt_pllocked);
assign mgt_rx_reset = reset156;
assign mgt_rx_reset = reset156 || ~mgt_plllocked;