uart-gb: convert over to the connection interface

Move the uart code over to use the "new" connection interface, instead
of the "old" module interface.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
uart-gb: remove global init functions

The uart-gb code needs to init the tty core before it can add devices.
Previously we hard-coded this in the greybus core, move this to be
"dynamic" and self-contained within the uart-gb.c file.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>