Do not complain about missing /dev/iphb by default

Having a kernel that supports iphb wakeups is a special case.

Not having it just means we are missing one wakeup source to synchronize
with i.e. no need to create noise about it on default verbosity level.

[iphb] Do not complain about missing /dev/iphb by default
Merge pull request #53 from spiiroin/iphb_device_warning

Do not complain about missing /dev/iphb by default