Broken watchdog in u-boot master branch

[Pali Rohár]

Hello! Watchdog code seems to be broken in u-boot master branch.
On Nokia N900 I'm getting following message in qemu:

cyclic function rx51_watchdog took too long: 10000us vs 1000us max, disabling

Seems that watchdog core code is not prepared for "slower" watchdogs
which communicate over slower i2c bus, like it is the case for N900.

Disabling slower watchdog is a bad idea as it would result in reboot
loop instead of slower - but working code.