[WATCHDOG] Freescale STMP: watchdog driver

Add watchdog timer support for Freescale STMP3xxx boards

Signed-off-by: Vitaly Wool <vital@embeddedalley.com>
Signed-off-by: Dmitry Pervushin <dpervushin@embeddedalley.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>