panfrost: Avoid accessing pan_pool fields directly

panfrost: Avoid accessing pan_pool fields directly

Having panfrost_batch access the pan_pool fields directly makes it hard
to change pan_pool internals, like for instance, changing the hash table
for a dynamic array. Let's hide pan_pool internals behind helpers that do
what we need.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6494>