lib: midi2: new UMP Stream responder library Add a new top-level, transport independent library to respond to UMP Stream Discovery messages. This allows MIDI2.0 clients to discover UMP endpoints hosted on Zephyr over the UMP protocol. The endpoint specification can be gathered from the device tree, so that the same information used to generate USB descriptors in usb-midi2.0 can be delivered over UMP Stream. Signed-off-by: Titouan Christophe <titouan.christophe@mind.be>