Clean up dataflash partitioning

This patch removes the board dependent parts from
"drivers/mtd/dataflash.c".
Each board relying on this, will have the appropriate
code in a new file, "partition.c" in the board directory.
board Makefiles updated to use the file.

The dataflash partitions are aligned on sector/page boundaries.

The CONFIG_NEW_DF_PARTITION was used to create named partitions
This is now the default operation, and the CONFIG variable is removed.

Signed-off-by: Ulf Samuelsson <ulf@atmel.com>