panfrost: Allow waiting on slots 6/7 during preload

panfrost: Allow waiting on slots 6/7 during preload

I don't understand the underlying uarch details but ATEST needs to wait
on slot 6 and BLEND needs to wait on both, so these bits are used if
ATEST/BLEND are in the first clause, which happens if e.g. a constant
colour is written, or if the input is preloaded.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8723>