We accomplished this by not connecting the trace pins. PTA6 (TRACE_CLKOUT), PTA7 (TRACE_D3), PTA8 (TRACE_D2), PTA9 (TRACE_D1), and PTA10 (TRACE_D0) were originally connected to the Cortex-M JTAG 20-pin debugger. If you are not using the JTAG trace capability, these pins do not need to be connected to the debugger. They can then be used for the flexbus. This makes connecting an external RAM to the flexbus possible and also use the RMII interface.