Rework DF to prepare for VBIOS that turns on channel hashing

[Joseph Greathouse]

When we start receiving Arcturus VBIOS that turns on channel hashing in the data fabric, we need to make sure that the texture cache's channel hashing setting match up. To do this, we query the DF's settings and cache them in adev, then mirror them into the cache confirmation on init.

This requires some rework of adev. Rather than just holding some function pointers, this series adds in a new DF data structure which will contain
the function pointer struct as well as any new structs we need. It then adds in the structs for holding the DF's current hash settings info.