drivers/fsi: Document FSI master sysfs files in ABI

Add info for sysfs scan file in Documentaiton ABI/testing
Signed-off-by: Christopher Bostic <cbostic@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-bus-fsi

+What:           /sys/bus/platform/devices/fsi-master/rescan
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        cbostic@linux.vnet.ibm.com
+Description:
+                Initiates a FSI master scan for all connected slave devices
+		on its links.
+
+What:           /sys/bus/platform/devices/fsi-master/break
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        cbostic@linux.vnet.ibm.com
+Description:
+		Sends an FSI BREAK command on a master's communication
+		link to any connnected slaves.  A BREAK resets connected
+		device's logic and preps it to receive further commands
+		from the master.
+
+What:           /sys/bus/platform/devices/fsi-master/slave@00:00/term
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        cbostic@linux.vnet.ibm.com
+Description:
+		Sends an FSI terminate command from the master to its
+		connected slave. A terminate resets the slave's state machines
+		that control access to the internally connected engines.  In
+		addition the slave freezes its internal error register for
+		debugging purposes.  This command is also needed to abort any
+		ongoing operation in case of an expired 'Master Time Out'
+		timer.
+
+What:           /sys/bus/platform/devices/fsi-master/slave@00:00/raw
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        cbostic@linux.vnet.ibm.com
+Description:
+		Provides a means of reading/writing a 32 bit value from/to a
+		specified FSI bus address.