soc: mediatek: cmdq: Use mailbox rx_callback instead of cmdq_task_cb

rx_callback is a standard mailbox callback mechanism and could cover the
function of proprietary cmdq_task_cb, so use the standard one instead of
the proprietary one. Client has changed to use the standard callback
machanism and sync dma buffer in client driver, so remove the proprietary
callback in cmdq helper.

Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Reviewed-by: jason-jh.lin <jason-jh.lin@mediatek.com>
Tested-by: jason-jh.lin <jason-jh.lin@mediatek.com>
Link: https://lore.kernel.org/r/1650102868-26219-1-git-send-email-chunkuang.hu@kernel.org


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>