dm: core: Pass a root node to of_find_node_by_phandle()

This function currently assumes that the control FDT is used. Update it
to allow a root node to be passed, so it can work with any tree.

Also add a comment to ofnode_get_by_phandle() so that its purpose is
clear.

Signed-off-by: Simon Glass <sjg@chromium.org>
4 files changed