usb: gadget: f_mass_storage: add configfs support

From this commit on f_mass_storage is available through configfs.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/Documentation/ABI/testing/configfs-usb-gadget-mass-storage b/Documentation/ABI/testing/configfs-usb-gadget-mass-storage
new file mode 100644
index 0000000..ad72a37
--- /dev/null
+++ b/Documentation/ABI/testing/configfs-usb-gadget-mass-storage
@@ -0,0 +1,31 @@
+What:		/config/usb-gadget/gadget/functions/mass_storage.name
+Date:		Oct 2013
+KenelVersion:	3.13
+Description:
+		The attributes:
+
+		stall		- Set to permit function to halt bulk endpoints.
+				Disabled on some USB devices known not to work
+				correctly. You should set it to true.
+		num_buffers	- Number of pipeline buffers. Valid numbers
+				are 2..4. Available only if
+				CONFIG_USB_GADGET_DEBUG_FILES is set.
+
+What:		/config/usb-gadget/gadget/functions/mass_storage.name/lun.name
+Date:		Oct 2013
+KenelVersion:	3.13
+Description:
+		The attributes:
+
+		file		- The path to the backing file for the LUN.
+				Required if LUN is not marked as removable.
+		ro		- Flag specifying access to the LUN shall be
+				read-only. This is implied if CD-ROM emulation
+				is enabled as well as when it was impossible
+				to open "filename" in R/W mode.
+		removable	- Flag specifying that LUN shall be indicated as
+				being removable.
+		cdrom		- Flag specifying that LUN shall be reported as
+				being a CD-ROM.
+		nofua		- Flag specifying that FUA flag
+				in SCSI WRITE(10,12)