scsi: ufs: Add dev ref clock gating wait time support

scsi: ufs: Add dev ref clock gating wait time support

In UFS version 3.0, a newly added attribute bRefClkGatingWaitTime defines
the minimum time for which the reference clock is required by device during
transition to LS-MODE or HIBERN8 state. Make this change to reflect the new
requirement by adding delays before turning off the clock.

Link: https://lore.kernel.org/r/1581392451-28743-7-git-send-email-cang@codeaurora.org
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>