UPSTREAM: scsi: ufs: ufs-mediatek: Refactor performance scaling functions

Refactor performance scaling related functions in MediaTek UFS driver.

Link: https://lore.kernel.org/r/20201116065054.7658-2-stanley.chu@mediatek.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>
(cherry picked from commit 54770cbe)
Bug: 204438323
Change-Id: I6a3ffc145bd404985a8d55680fb70ec7ad96b945
Signed-off-by: Bart Van Assche <bvanassche@google.com>