xen/arm: pass node to device_tree_for_each_node

xen/arm: pass node to device_tree_for_each_node

Add a new parameter to device_tree_for_each_node: node, the node to
start the search from.

To avoid scanning device tree, and given that we only care about
relative increments of depth compared to the depth of the initial node,
we set the initial depth to 0. Then, we call func() for every node with
depth > 0.

Don't call func() on the parent node passed as an argument. Clarify the
change in the comment on top of the function. The current callers pass
the root node as argument: it is OK to skip the root node because no
relevant properties are in it, only subnodes.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
[julien: Remove min_depth variable]
Acked-by: Julien Grall <julien.grall@arm.com>