zink: low portal-2-v2.trace perf on anv

I previous had a bug report looking at memory consumption, but I don't think that was really the problem.

zink is -29.4708% +/- 2.19994% compared to iris on fps of looping this trace for 3 seconds. If I disable PIPE_CAP_ALLOW_GLTHREAD_BUFFER_SUBDATA_OPT (that extremely dubious thing of issuing GPU copies for buffersubdatas that want to be just writing into BOs on this HW), then that gets us 19.882% +/- 1.38054% improvement.