BACKPORT: FROMGIT: scsi: ufshcd: Let vendor override devfreq parameters

Vendor drivers may have a need to update the polling interval and
thresholds.  Provide a vops for vendor drivers to use.

Bug: 152781094
(cherry picked from commit 2c75f9a5be53501a6e733cd72c1c46281eaa49a0
https://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git/log/?h=5.7/scsi-queue)
Link: https://lore.kernel.org/r/acd79e00396cff855256adad47f615ccdbde85ac.1585160616.git.asutoshd@codeaurora.org


Acked-by: Avri Altman <Avri.Altman@wdc.com>
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Change-Id: Iaa41b1861a95d686fa0db6d5b7eb045ed14b531f
[can: Resolved minor conflict in drivers/scsi/ufs/ufshcd.h ]
Signed-off-by: Can Guo <cang@codeaurora.org>