add OpenAMP driver

[mausys]

This pull request supersedes #79605. Only the RPMSG VirtIO-Device with the resource table is supported at the moment, but this is just a proof of concept.
The DTS for the rpmsg-virtio-device would look something like this:

chosen {. 
    ...
    openamp,resource-table = &rsc_tbl;
  };  
...
  mbox: mbox@40060000 {
...
  };

  vdev0vring0: memory@1400 {
    compatible= "zephyr,memory-region";
    zephyr,memory-region = "vdev0vring0";
    reg = <0x1400 0x2000>;
  };

  vdev0vring1: memory@3400 {
    compatible= "zephyr,memory-region";
    zephyr,memory-region = "vdev0vring1";
    reg = <0x3400 0x2000>;
  };

  vdev0buffer: memory@5400 {
    compatible= "zephyr,memory-region";
    zephyr,memory-region = "vdev0buffer";
    reg = <0x5400 0x8000>;
  };  

...

openamp {
    rsc_tbl: resource_table {
      compatible = "openamp,resource-table";
      carveouts = <&vdev0vring0 &vdev0vring1 &vdev0buffer>;
      vdevs = <&vdev0>;
    };

    vrings {
      #address-cells = <1>;
      #size-cells = <0>;

      vdev0_tx: vring@0 {
        compatible = "openamp,vring";
        #vring-cells = <0>;
        notify-id = <0>;
        memory-region = <&vdev0vring0>;
        num-buffers = <8>;
        mboxes = <&mbox 0>;
        reg = <0>;
      };

      vdev0_rx: vring@1 {
        compatible = "openamp,vring";
        #vring-cells = <0>;
        notify-id = <1>;
        memory-region = <&vdev0vring1>;
        num-buffers = <8>;
        mboxes = <&mbox 1>;
        reg = <1>;
      };
    };

    vdevs {
      #address-cells = <1>;
      #size-cells = <0>;

      vdev0: vdev@0 {
        compatible = "openamp,rpmsg-virtio-device";
        #address-cells = <1>;
        #size-cells = <0>;
        vrings = <&vdev0_tx &vdev0_rx>;
        vring-names = "tx", "rx";
        memory-region = <&vdev0buffer>;
        reg = <0>;
      };
    };
  };

Thoughts?