remoteproc: core: Introduce rproc_add_rvdev function

The rproc structure contains a list of registered rproc_vdev structure.
To be able to move the management of the rproc_vdev structure in
remoteproc_virtio.c (i.e rproc_rvdev_add_device function),
introduce the rproc_add_rvdev and rproc_remove_rvdev functions.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20220921135044.917140-3-arnaud.pouliquen@foss.st.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>