FPGA communicating with H-Bridge

So the first question would be do you see activity on the arduino header signal lines?

Do the PWMx lines toggle as expected (as viewed on a logic analyzer or oscilloscope)?

Is there SPI device communication with each of the selected motor control ICs? And is it as expected?

A logic analyzer with SPI protocol capability would be really useful for debug.

It could very well be your pin assignments are not correct (something simple to fix).

Or your internal code is not functioning correctly (more difficult debug).

Have you done a simulation of the design to verify your FPGA code is correctly operating?