Revert "drm/mediatek: Use mailbox rx_callback instead of cmdq_task_cb"

Revert "drm/mediatek: Use mailbox rx_callback instead of cmdq_task_cb"

This reverts commit c1ec54b7b5af25c779192253f5a9f05e95cb43d7.

Commit c1ec54b7b5af
("drm/mediatek: Use mailbox rx_callback instead of cmdq_task_cb")
would cause numerous mtk cmdq mailbox driver warning:

WARNING: CPU: 0 PID: 0 at drivers/mailbox/mtk-cmdq-mailbox.c:198
cmdq_task_exec_done+0xb8/0xe0

So revert that patch.

Reported-by: Enric Balletbo Serra <eballetbo@gmail.com>
Tested-by: Enric Balletbo Serra <eballetbo@gmail.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>