greybus: es2: add support for greybus cport flags

Add support for Greybus CPort flags that are sent to the bridge through
a new USB vendor request when enabling a CPort as part of connection
establishment.

Currently the Greybus control and high-priority connection flags are
recognised and forwarded to APBA.

Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>