freedreno/a6xx: Emit a WFI after event writes flushing CCU.

freedreno/a6xx: Emit a WFI after event writes flushing CCU.

Following on from !12475, do the same CCU workaround for freedreno as
turnip is doing, so that we flush CCU correctly for when color/depth is
next read under a different cache domain from where it was written.

Fixes instability (particularly if the GPU is clocked up) on
dEQP-GLES3.functional.fbo.blit.depth_stencil.depth32f_stencil8* in bypass
mode on a630.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11481>