MFC r323474, r323553, r323691

r323474:
Add a default implementation that returns ENODEV for start, repeat_start,
stop, read, and write methods. Some controllers don't implement these
individual operations and have only a transfer method. In that case, we
should return an indication that the device is present but doesn't support
the method, as opposed to the kobj default error ENXIO which makes it
look like the whole device is missing. Userland tools such as i2c(8) can
use the differing return values to switch between the two different i2c
IO mechanisms.

r323553:
Defer attaching and probing iicbus and its children until interrupts are
available, in i2c controller drivers that require interrupts for transfers.

This is the result of auditing all 22 existing drivers that attach iicbus.
These drivers were the only ones remaining that require interrupts and were
not using config_intrhook to defer attachment. That has led, over the
years, to various i2c slave device drivers needing to use config_intrhook
themselves rather than performing bus transactions in their probe() and
attach() methods, just in case they were attached too early.

r323691:
Give icee(4) a detach() method so it can be used as a module. Add a
module makefile for it.

Give icee(4) a detach() method so it can be used as a module. Add a
module makefile for it.