kern: switch various devfs_notify() callers to devfs_notifyf()

[kevans]

Summary

This is largely a simplification, avoiding extra allocations or string
manipulations where it's safe to do so (i.e., doesn't require extra
quoting).

[kevans]

I just noticed there's a devctl_notify(9) to update.

sys/dev/asmc/asmc.c

1358

I assumed the space here is insignificant and just gets absorbed as consecutive whitespace...

[imp]

I wish we had a way to validate that things were safe, though...
Maybe I'll add it after you commit this.

sys/dev/asmc/asmc.c

1358

correct.

[kevans]

Rebase and hit a few more devctl_notify() callers

vtterm_devctl(), in particular, becomes significantly less complicated as the
complexity of the operation moves into devctl_notifyf (where it would need to
allocate another sbuf, etc., even before devctl_notifyf was introduced).