Define a platform driver to manage the remoteproc virtio device as
a platform devices.

The platform device allows to pass rproc_vdev_data platform data to
specify properties that are stored in the rproc_vdev structure.

Such approach will allow to preserve legacy remoteproc virtio device
creation but also to probe the device using device tree mechanism.

remoteproc_virtio.c update:
  - Add rproc_virtio_driver platform driver. The probe ops replaces
    the rproc_rvdev_add_device function.
  - All reference to the rvdev->dev has been updated to rvdev-pdev->dev.
  - rproc_rvdev_release is removed as associated to the rvdev device.
  - The use of rvdev->kref counter is replaced by get/put_device on the
    remoteproc virtio platform device.
  - The vdev device no longer increments rproc device counter.
    increment/decrement is done in rproc_virtio_probe/rproc_virtio_remove
    function in charge of the vrings allocation/free.

remoteproc_core.c update:
  Migrate from the rvdev device to the rvdev platform device.
  From this patch, when a vdev resource is found in the resource table
  the remoteproc core register a platform device.
Signed-off-by: NArnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20220921135044.917140-5-arnaud.pouliquen@foss.st.comSigned-off-by: NMathieu Poirier <mathieu.poirier@linaro.org>