watchdog: use time_after_eq() in watchdog_reset()

watchdog: use time_after_eq() in watchdog_reset()

Some boards don't work with the rate-limiting done in the generic
watchdog_reset() provided by wdt-uclass.

For example, on powerpc, get_timer() ceases working during bootm since
interrupts are disabled before the kernel image gets decompressed, and
when the decompression takes longer than the watchdog device
allows (or enough of the budget that the kernel doesn't get far enough
to assume responsibility for petting the watchdog), the result is a
non-booting board.

As a somewhat hacky workaround (because DT is supposed to describe
hardware), allow specifying hw_margin_ms=0 in device tree to
effectively disable the ratelimiting and actually ping the watchdog
every time watchdog_reset() is called. For that to work, the "has
enough time passed" check just needs to be tweaked a little to allow
the now==next_reset case as well.

Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Stefan Roese <sr@denx.de>