freedreno: (Mostly) finish afuc decoding for a6xx, add tests

With this, we now decode every instruction in a630_sqe.fw, except for things that are actually data. The only things I know of that we're currently missing are:

• Flags on cwrite/cread/load/store. Currently we only know what one of them (0x4) does, but the firmware uses all 4, so this needs more RE.
• Printing pipe registers, like how we print control registers. This is complicated a bit by how the firmware frequently does mov $addr, 0xa204 << 16 which is actually something like mov $addr, ((NRT_DATA << 8) | 0x4) << 16 where the extra | 0x4 probably makes sure that successive writes to $data write to the same register (i.e. NRT_DATA). Getting the disassembler to spit out the decoded version of that, and properly assembling it, seems tricky.

Finally, now that we're more-or-less feature complete, add a mock a6xx firmware to test the assembly/disassembly.