Add missing profile=kvm option to Documentation/kernel-parameters.txt

Whilst looking up what profile=sleep did, I noticed that we missed
adding docs for the most recent addition to the profiler.

Signed-off-by: Dave Jones <davej@redhat.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Adrian Bunk <bunk@kernel.org>

Documentation/kernel-parameters.txt

@@ -1425,6 +1425,7 @@ and is between 256 and 4096 characters. It is defined in the file
 			Param: <number> - step/bucket size as a power of 2 for
 				statistical time based profiling.
 			Param: "sleep" - profile D-state sleeping (millisecs)
+			Param: "kvm" - profile VM exits.
 
 	processor.max_cstate=	[HW,ACPI]
 			Limit processor to maximum C-state