remoteproc: Introduce a sandbox dummy driver

remoteproc: Introduce a sandbox dummy driver

Introduce a dummy driver for sandbox that allows us to verify basic
functionality. This is not meant to do anything functional - but is
more or less meant as a framework plumbing debug helper.

The sandbox remoteproc driver maintains absolutey no states and is a
simple driver which just is filled with empty hooks. Idea being to give
an approximate idea to implement own remoteproc driver using this as a
template.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Simon Glass <sjg@chromium.org>