aco: Basic Navi support

This series adds support for Navi in aco_assembler, adds some Navi specific workarounds, and basically makes it possible to use ACO on Navi.

Note that not everything works perfectly yet, so I haven't actually enabled ACO by default on Navi yet. But the code here is already tested and ready for a thorough review. The subgroup patches will come in a later MR.