davinci: dm646x-evm: Add platform data for NAND

This patch adds platform data and partition info for NAND on dm6467 EVM.

Note that the partition layout is dependent on the UBL, U-Boot etc. used. This
patch tries to minimize that dependency by setting first partition for UBL,
U-Boot and environment altogether.

Signed-off-by: Hemant Pedanekar <hemantp@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>