Even the open Unix projects has big problems with this because of the lack of documentation. PowerVR and Mali I guess are the chips one would be looking into.
So the documentation is in essence one early step to evaluate the feasibility.
When you start thinking about those GPUs, and the fact that they are often incorporated into ARM processors, then the next logical step is full emulation.
So why connect it to an Amiga?
Kronos is right.
It is simpler to move to an NG system.