watchdog: cortina_wdt: add support for HW WDT on CAxxxx SoCs

Add support for hardware watchdog timer on all Cortina Access
CAxxxx family of SoCs.

Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Jason Li <jason.li@cortina-access.com>
Signed-off-by: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>