Staging: ipack: improve the register of a bus and a device in the bus.

It adds and removes some fields in the struct ipack_device and
ipack_bus_device to make it cleaner.

The API has change to group all the operations on these structures inside
of the ipack driver.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>