greybus: interface: s/gb_interface_block/gb_interface/g

Rename struct gb_interface_block to struct gb_interface

Lots of renaming, and variable renames as well (gb_ib->intf), but all
should be sane with regards to the new naming scheme we are using.

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