scsi: ufs-mediatek: introduce reference clock control

Introduce reference clock control in MediaTek Chipset in order to disable
it if it is not necessary by UFS device to save system power.

Currently reference clock can be disabled during system suspend, runtime
suspend and clock-gating after link enters hibernate state.

Cc: Alim Akhtar <alim.akhtar@samsung.com>
Cc: Avri Altman <avri.altman@wdc.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Bean Huo <beanhuo@micron.com>
Cc: Can Guo <cang@codeaurora.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/1577683950-1702-4-git-send-email-stanley.chu@mediatek.com


Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>