scsi: ufs: ufs-mediatek: Support clk-scaling to optimize power consumption

Provide clk-scaling feature in MediaTek UFS platforms.

MediaTek platform supports clk-scaling by switching parent clock mux of
UFSHCI main clocks: ufs_sel.

The driver needs to prevent changing the rate of ufs_sel because its parent
PLL clock may be shared between multiple IPs. In order to achieve this
goal, the maximum and minimum clock rates of ufs_sel defined in dts should
match the rate of "ufs_sel_max_src" and "ufs_sel_min_src" respectively.

Link: https://lore.kernel.org/r/20220802235437.4547-6-stanley.chu@mediatek.com


Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Po-Wen Kao <powen.kao@mediatek.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>