[WATCHDOG] Fix booke_wdt.c on MPC85xx SMP system's

On Book-E SMP systems each core has its own private watchdog.  If only one
watchdog is enabled, when the core that doesn't enable the watchdog is hung,
system can't reset because no watchdog is running on it.  That's bad.  It
means we must enable watchdogs on both cores.

We can use smp_call_function() to send appropriate messages to all the other
cores to enable and update the watchdog.

Signed-off-by: Chen Gong <g.chen@freescale.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>