So far, wd has always configured the highest-priority watchdog when
multiple are available. Add an optional -d parameter to support
configuring the other watchdogs as well. The name passed can be either
the watchdog device name (e.g. wdog0) or the hardware device name (e.g.
efi-wdt).

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>