watchdog: Integrate watchdog triggering into the cyclic framework

This patch integrates the watchdog triggering into the recently added
cyclic infrastructure. Each watchdog device that shall be triggered
registers it's own cyclic function. This way, multiple watchdog devices
are still supported, each via a cyclic function with separate trigger
intervals.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Tom Rini <trini@konsulko.com> [am335x_evm, mx6cuboxi, rpi_3,dra7xx_evm, pine64_plus, am65x_evm, j721e_evm]