OF: base: convert and remove device_node_for_nach_child

Remove device_node_for_nach_child and convert users to corresponding
imported OF API functions.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
OF: base: export of_alias_scan

To prepare clean-up of OF API, we need to also export of_alias_scan.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
OF: base: import property iterators from Linux OF API

This imports of_prop_next_u32, of_prop_next_string, and the corresponding
for_property_for_each_ helpers from Linux OF API.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>