dm: core: Add functions to obtain node's address/size cells

The of_n_addr_cells() and of_n_size_cells() functions are useful for
getting the size of addresses in a node, but in a few places U-Boot needs
to obtain the actual property value for a node without walking up the
stack. Add functions for this and just the existing code to use it.

Add a comment to the existing ofnode functions which do not do the right
thing with a flat tree.

This fixes a problem reading PCI addresses.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-on: Beaver, Jetson-TK1
diff --git a/drivers/core/regmap.c b/drivers/core/regmap.c
index 749d913..d4e16a2 100644
--- a/drivers/core/regmap.c
+++ b/drivers/core/regmap.c
@@ -72,8 +72,8 @@
 	ofnode node = dev_ofnode(dev);
 	struct resource r;
 
-	addr_len = dev_read_addr_cells(dev->parent);
-	size_len = dev_read_size_cells(dev->parent);
+	addr_len = dev_read_simple_addr_cells(dev->parent);
+	size_len = dev_read_simple_size_cells(dev->parent);
 	both_len = addr_len + size_len;
 
 	len = dev_read_size(dev, "reg");