remoteproc: Introduce rproc handle accessor for children

In certain circumstances rpmsg devices needs to acquire a handle to the
ancestor remoteproc instance, e.g. to invoke rproc_report_crash() when a
fatal error is detected. Introduce an interface that walks the device
tree in search for a remoteproc instance and return this.

Tested-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

include/linux/remoteproc.h

@@ -510,6 +510,8 @@ struct rproc_vdev {
 };
 
 struct rproc *rproc_get_by_phandle(phandle phandle);
+struct rproc *rproc_get_by_child(struct device *dev);
+
 struct rproc *rproc_alloc(struct device *dev, const char *name,
 			  const struct rproc_ops *ops,
 			  const char *firmware, int len);