of/fdt: Scan the root node properties earlier
Scan the root node properties (#{size,address}-cells) earlier, so that
the dt_root_addr_cells and dt_root_size_cells variables are initialized
and can be used.
Link: https://lore.kernel.org/all/20180830190523.31474-2-robh@kernel.org/
Signed-off-by: Rob Herring <robh@kernel.org>