greybus: es2: add define for ARPC CPort requests

Add dedicated define for ARPC CPort requests instead of using the
default timeout for USB vendor requests.

We still allow responses to take 500 ms to arrive, but note that this
adds on top of the 500ms already allowed for a requests to be
acknowledged. This should probably be tightened up at some point.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>