panfrost: Prepare for bifrost compiler tests

We'd like to run compiler tests without Gallium's involvement, so let's move some of the core BO management etc code to root panfrost. From there, we start building up a vertex job to test the compiler. The later code doesn't actually work quite yet, since we're getting faults. I'm not sure if the issue is the command stream we're passing or kernel-related, so while the kernel is investigated I'm holding off on too much further debug. (So let's merge this now before the churn goes stale.)