dm: core: add ofnode and dev function to iterate on node property

Add functions to iterate on all property with livetree
- dev_read_first_prop
- dev_read_next_prop
- dev_read_prop_by_prop
and
- ofnode_get_first_property
- ofnode_get_next_property
- ofnode_get_property_by_prop

And helper: dev_for_each_property

For example:
struct ofprop property;

dev_for_each_property(property, config) {
	value = dev_read_prop_by_prop(&property, &propname, &len);

or:

for (res = ofnode_get_first_property(node, &property);
     !res;
     res = ofnode_get_next_property(&property))
{
     value = ofnode_get_property_by_prop(&property, &propname, &len);
....
}

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index f55874c..6c18fd0 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -31,8 +31,9 @@
 obj-$(CONFIG_LED) += led.o
 obj-$(CONFIG_DM_MAILBOX) += mailbox.o
 obj-$(CONFIG_DM_MMC) += mmc.o
-obj-y += ofnode.o
 obj-y += fdtdec.o
+obj-y += ofnode.o
+obj-y += ofread.o
 obj-$(CONFIG_OSD) += osd.o
 obj-$(CONFIG_DM_VIDEO) += panel.o
 obj-$(CONFIG_DM_PCI) += pci.o