Staging: ipack/devices/ipoctal: split ipoctal_channel from ipoctal.

By moving everything channel related into a separate struct we will be
able to clean up a lot of code.  In the end tty->driver_data will no
longer need to point to ipoctal but instead can point to the respective
channel.
Signed-off-by: Jens Taprogge <jens.taprogge@taprogge.org>
Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>