i2c: i2c stack can remove()

More update for new style driver support:  add a remove() method, and
use it in the relevant code paths.

Again, nothing will use this yet since there's nothing to create devices
feeding this infrastructure.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>