Device Tree really improves code maintainability and is now
available for SPL too.

This is the state-of-the-art implementation in U-boot.

The board files (platform data) are no longer needed.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: NMarek Vasut <marex@denx.de>
Reviewed-by: NSimon Glass <sjg@chromium.org>