panfrost: Fix discard behaviour on Bifrost

Set zs_update_operation to FORCE_LATE, as we don't want to update
depth if the fragment is discarded.

Set pixel_kill_operation to WEAK_EARLY to match the blob.

Reviewed-and-tested-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <!8235>
41 jobs for !8235 with discard in 9 minutes and 18 seconds (queued for 3 seconds)
merge request