greybus: interface: separate manifest parsing from bundle registration

Separate manifest parsing, including bundle and connection creation,
from bundle registration.

Note that this is also needed to allow the interface to not be
registered until the manifest has been parsed.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>