greybus: fix cport-id defines

The CPORT_ID_MAX define has been used by host drivers as a device limit,
but also for sanity checks when parsing manifests.

Now that it's only used for sanity checks we can increase it to the
specification maximum (4095) and get rid of the config-option that could
be used to override the previous limit (128).

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