Documentation: Add ABI entry for crash_notes and crash_notes_size

Add an Documentation/ABI entry for /sys/devices/system/cpu/cpu0/crash_notes
and /sys/devices/system/cpu/cpu0/crash_notes_size.

Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-devices-system-cpu

@@ -173,3 +173,15 @@ Description:	Processor frequency boosting control
 		Boosting allows the CPU and the firmware to run at a frequency
 		beyound it's nominal limit.
 		More details can be found in Documentation/cpu-freq/boost.txt
+
+
+What:		/sys/devices/system/cpu/cpu#/crash_notes
+		/sys/devices/system/cpu/cpu#/crash_notes_size
+Date:		April 2013
+Contact:	kexec@lists.infradead.org
+Description:	address and size of the percpu note.
+
+		crash_notes: the physical address of the memory that holds the
+		note of cpu#.
+
+		crash_notes_size: size of the note of cpu#.