i.MX: Add code to emulate i.MX2 watchdog IP block

i.MX: Add code to emulate i.MX2 watchdog IP block

Add enough code to emulate i.MX2 watchdog IP block so it would be
possible to reboot the machine running Linux Guest.

Cc: Peter Maydell <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Philippe Mathieu-Daudé <[email protected]>
Cc: Marcel Apfelbaum <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Andrey Smirnov <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>