greybus: es2.c: add a control request for endpoints mapping

ES2 give us more endpoints. Use them to map one cport to two endpoints
(in and out). Because there is more cports than endpoints, we still
need to mux other cports traffic on 2 endpoints.
Firmware currently assumes these endpoints are 2 and 3.

By default, all cports are muxed.
To map one cport to 2 endpoints, use map_cport_to_ep().

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>