remoteproc: add actual recovery implementation

Add rproc_trigger_recovery() which takes care of the recovery itself,
by removing, and re-adding, all of the remoteproc's virtio devices.

This resets all virtio users of the remote processor, during which
the remote processor is powered off and on again.

Signed-off-by: Fernando Guzman Lugo <fernando.lugo@ti.com>
[ohad: introduce rproc_add_virtio_devices to avoid 1.copying code 2.anomaly]
[ohad: some white space, naming and commit log changes]
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>