u can convert only filters in to VHDL (from matlab format )in matlab software. if u want to convert the matlab code to vhdl or verilog code then u have to install Xilinx accel dsp. which u may get a trail version for 30 days and try on it first.
then go for licenced version. from www.xilinx.com
Could you generate VHDL form Simulink? Wich Blocks are working? How bugged it is?
I once generated C code form Simulink to run on a microcontroller, it worked very well for DSP and finite state machine.