At this point remoteproc can only register a single VIRTIO_ID_RPMSG virtio
device.

This limitation is going away soon: remoteproc is getting support for
registering any number of virtio devices and of any type (as
published by the firmware of the remote processor).

Rename remoteproc_rpmsg.c to remoteproc_virtio.c in preparation of
this generalization work.

Signed-off-by: Ohad Ben-Cohen
Cc: Brian Swetland
Cc: Iliyan Malchev
Cc: Arnd Bergmann
Cc: Grant Likely
Cc: Rusty Russell
Cc: Mark Grosen
Cc: John Williams
Cc: Michal Simek
Cc: Loic PALLARDY
Cc: Ludovic BARRE
Cc: Omar Ramirez Luna
Cc: Guzman Lugo Fernando
Cc: Anna Suman
Cc: Clark Rob
Cc: Stephen Boyd
Cc: Saravana Kannan
Cc: David Brown
Cc: Kieran Bingham
Cc: Tony Lindgren