greybus: es2: Reserve CPorts 16 and 17

CPorts 16 and 17 are reserved for CDSI0 and CDSI1 by the ES2 APB, make
sure they won't be allocated dynamically.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>