HWMON: coretemp, suspend fix

It's not permitted to unregister a device after devices have been suspended.
It causes deadlocks to appear on systems with coretemp hwmon loaded.  To avoid
this, we can make coretemp_cpu_callback() do nothing if the _FROZEN bit is set
in action.
 
Also, in other cases it's generally too late to unregister the coretemp device
if the CPU is already dead, so it should be unregistered on CPU_DOWN_PREPARE.
 
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Mark M. Hoffman <mhoffman@lightlink.com>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>