Watchdog on RPi and watchdogd

[Samorukov,Alexey]

Hi, 

I tried to use watchdogd on RPi 1. Initially i got "patting the dog: Operation not supported” and "Can't arm, timeout must be between 1-15 seconds”. Digging into the source i found that it is hardware limitation and i been able to run the watchdog correctly using "watchdogd -d -s 1 -t 8”. However it gives me only 8 seconds (2^33) and i would like to have 15. But if i am trying to set 15, watchdogd using 2^34 (17 seconds) and fail because its > 15, which is hw limit.

So in fact using current interface i can use maximum 8 seconds instead of possible 15. I think it should be viable solution to limit value to 15 seconds (with warning in the logs) in the bcmwd driver if request is > 15 seconds instead of warning. This should give ability to utilize maximum timeout with the old API. I can send a PR if there are no objections against this.