remoteproc: core: Introduce rproc_rvdev_add_device function

remoteproc: core: Introduce rproc_rvdev_add_device function

In preparation of the migration of the management of rvdev in
remoteproc_virtio.c, this patch spins off a new function to manage the
remoteproc virtio device creation.

The rproc_rvdev_add_device will be moved to remoteproc_virtio.c.

The rproc_vdev_data structure is introduced to provide information for
the rvdev creation. This structure allows to manage the rvdev and vrings
allocation in the rproc_rvdev_add_device function.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20220921135044.917140-2-arnaud.pouliquen@foss.st.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>