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 d4377f43afa93d81f4e789a58a2c820083b4c85d.

Commit d4377f43afa9
("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>