To support driver model and device tree, use the SPI-flash-based
AT45xxx DataFlash driver, DataFlash is a kind of SPI flash.
Instead of ATMEL_DATAFLASH_SPI DataFlash older driver that will
be removed in the future.

Signed-off-by: Wenyou Yang <wenyou.yang@microchip.com>
Reviewed-by: Simon Glass <sjg@chromium.org>