staging: fsl-mc: add sysfs ABI doc

define the bind/unbind sysfs interfaces for the fsl-mc bus
Signed-off-by: NStuart Yoder <stuart.yoder@nxp.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-bus-fsl-mc

+What:		/sys/bus/fsl-mc/drivers/.../bind
+Date:		December 2016
+Contact:	stuart.yoder@nxp.com
+Description:
+		Writing a device location to this file will cause
+		the driver to attempt to bind to the device found at
+		this location. The format for the location is Object.Id
+		and is the same as found in /sys/bus/fsl-mc/devices/.
+                For example:
+		# echo dpni.2 > /sys/bus/fsl-mc/drivers/fsl_dpaa2_eth/bind
+
+What:		/sys/bus/fsl-mc/drivers/.../unbind
+Date:		December 2016
+Contact:	stuart.yoder@nxp.com
+Description:
+		Writing a device location to this file will cause the
+		driver to attempt to unbind from the device found at
+		this location. The format for the location is Object.Id
+		and is the same as found in /sys/bus/fsl-mc/devices/.
+                For example:
+		# echo dpni.2 > /sys/bus/fsl-mc/drivers/fsl_dpaa2_eth/unbind