mmc: mtk-sd: Add wait dma stop done flow

mmc: mtk-sd: Add wait dma stop done flow

We found this issue on a 5G platform, during CMDQ error handling, if DMA
status is active when it call msdc_reset_hw(), it means mmc host hw reset
and DMA transfer will be parallel, mmc host may access sram region
unexpectedly. According to the programming guide of mtk-sd host, it needs
to wait for dma stop done after set dma stop.

This change should be applied to all SoCs.

Signed-off-by: Derong Liu <derong.liu@mediatek.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210827071537.1034-1-derong.liu@mediatek.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>