scsi: ufs-mediatek: Customize WriteBooster flush policy

Change the WriteBooster policy to keep VCC on during runtime suspend if
available WriteBooster buffer is less than 80%.

Link: https://lore.kernel.org/r/20200509093716.21010-5-stanley.chu@mediatek.comReviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ufs/ufs-mediatek.c

@@ -271,6 +271,7 @@ static int ufs_mtk_init(struct ufs_hba *hba)
 
 	/* Enable WriteBooster */
 	hba->caps |= UFSHCD_CAP_WB_EN;
+	hba->vps->wb_flush_threshold = UFS_WB_BUF_REMAIN_PERCENT(80);
 
 	/*
 	 * ufshcd_vops_init() is invoked after