feat(fdt-wrappers): add function to find or add a sudnode

This change adds a new utility function - `fdtw_find_or_add_subnode`
to find a subnode. If the subnode is not present, the function adds
it in the flattened device tree.

Signed-off-by: Ruchika Gupta <ruchika.gupta@linaro.org>
Change-Id: Idf3ceddc57761ac015763d4a8b004877bcad766a
2 files changed