test: dm: fix broken dm_test_ofnode_phandle_ot and get_by_phandle_ot

test: dm: fix broken dm_test_ofnode_phandle_ot and get_by_phandle_ot

Fix broken dm_test_ofnode_phandle_ot test. They never actually worked
and were passing test by pure luck by having the same phandle index of
test.dts that coincicentally had #gpio-cells in the same index node.

It was sufficient to add a phandle to test.dts to make the test fail.

To correctly test these feature, make use oif the new OPs oftree to
parse phandle.

For consistency with the dm_test_ofnode_phandle, rework the test and
other.dts to use the same property with the other- prefix to every
node.

Also fix dm_test_ofnode_get_by_phandle_ot by making it more robust and
renaming the phandle property to other-phandle.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>