of: define of_find_node_by_phandle for !CONFIG_OF

Define stub implementation for of_find_node_by_phandle() API
so that users of this API can build properly even when CONFIG_OF
is not defined.

Fixes x86 randconfig build failure of remoteproc.

Signed-off-by: Suman Anna <s-anna@ti.com>
[robh: add details on fixing remoteproc compile]
Signed-off-by: Rob Herring <robh@kernel.org>