Add a driver for Independent Watchdog (IWDG) commonly found in STM32
MCUs. The driver has been tested on STM32F1 family MCU.
Change-Id: Idc6ac35990e46901a206b4af0ce3767eb4875de9
Origin: Original
Signed-off-by: Maciej Borzecki <maciek.borzecki@gmail.com>