panfrost: Stop using panfrost_bo_release() outside of pan_bo.c

panfrost: Stop using panfrost_bo_release() outside of pan_bo.c

panfrost_bo_unreference() should be used instead.

The only difference caused by this change is that the scratchpad,
tiler_heap and tiler_dummy BOs are now returned to the cache instead
of being freed when a context is destroyed. This is only a problem if
we care about context isolation, which apparently is not the case since
transient BOs are already returned to the per-FD cache (and all contexts
share the same address space anyway, so enforcing context isolation
is almost impossible).

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>