pvr: fixup transfer primary sub-command list

pvr: fixup transfer primary sub-command list

When we allocate a new primary sub-command of type
PVR_SUB_CMD_TYPE_TRANSFER we need to make sure the list backing
transfer sub-commands can be shared and managed by both the
secondary and primary sub-command. Do this by always using a
pointer to maintain the list.

Found with:
  dEQP-VK.memory.pipeline_barrier.host_write_transfer_src.8192

Signed-off-by: Luigi Santivetti <luigi.santivetti@imgtec.com>
Reported-by: Frank Binns <frank.binns@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23918>