panfrost: Don't set shared->unk0

panfrost: Don't set shared->unk0

This field controls the size of per-thread temporaries (somehow this is
separate from the regular stack for register spilling..), though I'm not
certain on the details. Regardless this value of 0x1e despite being used
in places by the blob seems wrong and is interfering with correct sizing
of the stack.

We don't use non-spilling scratchpad yet, so this is just here to fix
some details of spilling.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3950>