amd/common: derive register headers and ac_debug from a JSON database

Move to a description of registers in a JSON file as the single source of truth for register descriptions. Both register headers and the tables used for decoding command buffers for debugging are derived from this JSON description at build time.

This should make ac_debug less fragile down the line, and allows us to be more explicit about which chips have which registers / fields / enum values.

The JSON description also has a notion of address spaces. This is already used to distinguish packet3 payloads from registers, and could be used in the future to distinguish more cleanly between registers and resource descriptor fields as well.