vc4: Add support for dumping executed commands to a file.

vc4: Add support for dumping executed commands to a file.

The VC4_DEBUG=cl,qpu is nice and all, but I want to be able to get more
detailed dumps, and to replay the same exact commands in simulation.  For
that I need a dump with all of the VBOs, shaders, shader recs, etc.  This
dump can be parsed by vc4-gpu-tools.

For now this is only doable from simulator mode, because otherwise we
don't have access to the RCL contents generated by the kernel.