freedreno/registers: reg64 decoding improvements and cleanup bindless-base register definitions

This started as wanting to less sloppily define the bindless-base regs, which turned into a bit of a rabbit-hole of improving reg64 decoding. But I like the result and it also turned up what is either a bug in the kernel devcore register snapshotting or a gap in our understanding about how to decode CLUSTER_PS. (See https://patchwork.freedesktop.org/series/112302/)