scsi: ufs: docs: ABI: Add wb_on documentation for new entry wb_on

Adds UFS sysfs documentation for new entry wb_on.

[mkp: fix doc formatting]

Link: https://lore.kernel.org/r/20210119163847.20165-3-huobean@gmail.com
Signed-off-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

fix format

Documentation/ABI/testing/sysfs-driver-ufs

@@ -1153,3 +1153,14 @@ Description:	This entry shows the configured size of WriteBooster buffer.
 		0400h corresponds to 4GB.
 
 		The file is read only.
+
+What:		/sys/bus/platform/drivers/ufshcd/*/wb_on
+Date:		January 2021
+Contact:	Bean Huo <beanhuo@micron.com>
+Description:	This node is used to set or display whether UFS WriteBooster is
+		enabled. Echo 0 to this file to disable UFS WriteBooster or 1 to
+		enable it. The WriteBooster is enabled after power-on/reset,
+		however, it will be disabled/enable while CLK scaling down/up
+		(if the platform supports UFSHCD_CAP_CLK_SCALING). For a
+		platform that doesn't support UFSHCD_CAP_CLK_SCALING, we can
+		disable/enable WriteBooster through this sysfs node.