Make this driver a user of the watchdog framework and remove parts now handled
by the core. Tested on a custom lpc32xx-board.

[wim@iguana.be: Added set_timeout operation]
Signed-off-by: NWolfram Sang <w.sang@pengutronix.de>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>