asahi: Coherency fixes for G13X

This fixes the CDM coherency, tested on G13D.

This turned out to only affect G13X and not G14X, as the bit is only needed there. G14C is definitely fine. It would be good to test this on G14D too, though I think that logically speaking, it should work (the only G14D difference we'd identified previously is the one for atomics that is still in place, so assuming XFB used to work this also should). I left the if tree in place with the commented out bits, in case we ever need to flip those for some other reason, assuming the device-specific logic is the same as it was for XFB.

There is an unrelated kernel issue with layered rendering + clustering that needs a kernel-side fix for CTS to not regress with recent Mesa changes on G13X and G14X.