remoteproc: Refactor function rproc_free_vring()

When function rproc_free_vring() clears the virtio device section
it does so on the cached resource table rather than the one
installed in the remote processor memory.  When a remote processor
has been booted by another entity there is no need to use a cached
table and as such, no need to clear the virtio device section in
it.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Link: https://lore.kernel.org/r/20200714195035.1426873-9-mathieu.poirier@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>