watchdog: wdt-uclass.c: handle all DM watchdogs in watchdog_reset()

watchdog: wdt-uclass.c: handle all DM watchdogs in watchdog_reset()

A board can have and make use of more than one watchdog device, say
one built into the SOC and an external gpio-petted one. Having
wdt-uclass only handle the first is both a little arbitrary and
unexpected.

So change initr_watchdog() so we visit (probe) all DM watchdog
devices, and call the init_watchdog_dev helper for each.

Similarly let watchdog_reset() loop over the whole uclass - each
having their own ratelimiting metadata, and a separate "is this device
running" flag.

This gets rid of the watchdog_dev member of struct global_data.  We
do, however, still need the GD_FLG_WDT_READY set in
initr_watchdog(). This is because watchdog_reset() can get called
before DM is ready, and I don't think we can call uclass_get() that
early.

The current code just returns 0 if "getting" the first device fails -
that can of course happen because there are no devices, but it could
also happen if its ->probe call failed. In keeping with that, continue
with the handling of the remaining devices even if one fails to
probe. This is also why we cannot use uclass_probe_all().

If desired, it's possible to later add a per-device "u-boot,autostart"
boolean property, so that one can do CONFIG_WATCHDOG_AUTOSTART
per-device.

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>