scsi: ufs: ufs-mediatek: support linkoff state during suspend

scsi: ufs: ufs-mediatek: support linkoff state during suspend

If system suspend or runtime suspend mode is configured as linkoff state,
phy can be powered off and reference clock can be gated in MediaTek
Chipsets.

At the same time, remove redundant reference clock control in suspend and
resume callbacks because such control can be well-handled in setup_clocks
callback.

Link: https://lore.kernel.org/r/20200129105251.12466-3-stanley.chu@mediatek.com
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>