watchdog: convert drivers/watchdog/* to use module_platform_driver_probe

This makes the code a bit smaller by getting rid of
some boilerplate code.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>