of: Add self test for of_match_node()

Adds a selftest function for the of_match_node function. of_match_node
is supposed to handle precedence for the compatible property as well as
the name and device_type values. This patch adds some test case data and
a function that makes sure each test node matches against the correct
entry of an of_device_id table.

This code was written to verify the new of_match_node() implementation
that is an earlier part of this series.

Signed-off-by: Grant Likely <grant.likely@linaro.org>
Cc: Kevin Hao <haokexin@gmail.com>