of: unittest: Add phandle remapping test

Test the functionality of of_parse_phandle_with_args_map().

Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>