bundle: s/gb_interface/gb_bundle/g

Rename struct gb_interface to struct gb_bundle

It's a lot of renaming, some structures got renamed and also some
fields, but the goal was to rename things to make sense with the new
naming of how the system is put together in the 'driver model' view.

Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>