watchdog: NXP LPC18xx Watchdog Timer Driver

This commit adds support for the watchdog timer found in NXP LPC SoCs
family, which includes LPC18xx/LPC43xx. Other SoCs in that family may
share the same watchdog hardware.

Watchdog driver registers a restart handler that will restart the system
by performing an incorrect feed after ensuring the watchdog is enabled in
reset mode.

As watchdog cannot be disabled in hardware, driver's stop routine will
regularly send a keepalive ping using a timer.

Signed-off-by: Ariel D'Alessandro <ariel@vanguardiasur.com.ar>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>