BACKPORT: scsi: ufs: Introduce event_notify variant function

Introduce event_notify variant function to allow vendor to get notification
of important events and connect to any proprietary debugging facilities.

Bug: 188004633
Change-Id: I7e23fb0842c1c114be97286627ea1c241d66ea31
(cherry picked from commit 172614a9)
[Stanley: Resolved minor conflict in drivers/scsi/ufs/ufshcd.c]
Link: https://lore.kernel.org/r/20201205115901.26815-4-stanley.chu@mediatek.com


Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Reviewed-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>