the watchdog hwdev is usually named with devicetree schema
which is not practical for CLI.

On device registration "wdog" will be extended with some index number
extracted from devicetree (if awailable) or automatically assigned
first available number. End result will be "wdog0" .. etc.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>