watchdog: Update documentation

The soft and hard lockup detectors are now built on top of the
hrtimer and perf subsystems. Update the documentation
accordingly.

Signed-off-by: Fernando Luis Vazquez <Cao&lt;fernando@oss.ntt.co.jp>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Link: http://lkml.kernel.org/r/1328827342-6253-1-git-send-email-dzickus@redhat.com


Signed-off-by: Ingo Molnar <mingo@elte.hu>