Add some definitions and helpers for livetree in the main of.h header
file. These include:

- reading multi-cell integers
- default number of address/size cells
- functions for comparing names

Signed-off-by: Simon Glass <sjg@chromium.org>

These two functions have an of_ prefix which conflicts with naming used
in of_addr. Rename them:

   fdt_read_number
   fdt_support_bus_default_count_cells

Signed-off-by: Simon Glass <sjg@chromium.org>

Add functions to add addresses in the device tree using ofnode references.

Signed-off-by: Simon Glass <sjg@chromium.org>

Since U-Boot supports both a live tree and a flat tree, we need an easy
way to access the tree without worrying about which is currently active.
To support this, U-Boot has the concept of an ofnode, which can refer
either to a live tree node or a flat tree node.

For the live tree, the reference contains a pointer to the node (struct
device_node *) or NULL if the node is invalid. For the flat tree, the
reference contains the node offset or -1 if the node is invalid.

Add a basic set of operations using ofnodes. These are implemented by
using either libfdt functions (in the case of a flat DT reference) or
the live-tree of_...() functions.

Note that it is not possible to have both live and flat references active
at the same time. As soon as the live tree is available, everything in
U-Boot should switch to using that. This avoids confusion and allows us to
assume that the type of a reference is simply based on whether we have a
live tree yet, or not.

Signed-off-by: Simon Glass <sjg@chromium.org>