fdt: call fdt_parent_offset fewer times while translating addresses

fdt_parent_offset() is an expensive operation, so we'd like to reduce
unnecessary calls to it.

Further, the practice of iterating up to the root if address/size cells
aren't found was apparently done for Linux for compatibility with certain
buggy Open Firmware implementations, and U-Boot inherited the code.  The
compliant behavior is to treat a missing #address-cells as 2, and a missing
#size-cells as 1 -- never looking anywhere but the immediate parent of the
node of interest.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>