cmd_nand: dump: Align data and OOB buffers

In order for cache invalidation and flushing to work properly, the data
and OOB buffers must be aligned to full cache lines.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>