mei: sysfs: add Documentation mei class attributes

Add sysfs attributes Documentation entries
for /sys/class/mei
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-class-mei

+What:		/sys/class/mei/
+Date:		May 2014
+KernelVersion:	3.17
+Contact:	Tomas Winkler <tomas.winkler@intel.com>
+Description:
+		The mei/ class sub-directory belongs to mei device class
+
+
+What:		/sys/class/mei/meiN/
+Date:		May 2014
+KernelVersion:	3.17
+Contact:	Tomas Winkler <tomas.winkler@intel.com>
+Description:
+		The /sys/class/mei/meiN directory is created for
+		each probed mei device
+