mei: add ABI documentation for fw_status exported through sysfs

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-class-mei

@@ -14,3 +14,18 @@ Description:
 		The /sys/class/mei/meiN directory is created for
 		each probed mei device
 
+What:		/sys/class/mei/meiN/fw_status
+Date:		Nov 2014
+KernelVersion:	3.19
+Contact:	Tomas Winkler <tomas.winkler@intel.com>
+Description:	Display fw status registers content
+
+		The ME FW writes its status information into fw status
+		registers for BIOS and OS to monitor fw health.
+
+		The register contains running state, power management
+		state, error codes, and others. The way the registers
+		are decoded depends on PCH or SoC generation.
+		Also number of registers varies between 1 and 6
+		depending on generation.
+