arch/*: Kconfig: fix documentation for NMI watchdog

Changeset 9919cba7ff ("watchdog: Update documentation") updated
the documentation, removing the old nmi_watchdog.txt and adding
a file with a new content.

Update Kconfig files accordingly.

Fixes: 9919cba7ff ("watchdog: Update documentation")

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Jonathan Corbet <corbet@lwn.net>

arch/sh/Kconfig

@@ -687,7 +687,7 @@ config SMP
 	  People using multiprocessor machines who say Y here should also say
 	  Y to "Enhanced Real Time Clock Support", below.
 
-	  See also <file:Documentation/nmi_watchdog.txt> and the SMP-HOWTO
+	  See also <file:Documentation/lockup-watchdogs.txt> and the SMP-HOWTO
 	  available at <http://www.tldp.org/docs.html#howto>.
 
 	  If you don't know what to do here, say N.