davinci: dm644x evm: setup NAND flash timing

The DM644x EVM nand flash timing was earlier being
done as a special case in the NAND driver itself.

With the NAND driver now capable of progamming the
AEMIF interface using timing data passed from the
platform, the timing values are being moved into
their rightful place in the EVM specific board file.

The values being programmed match what was being done
earlier and thus do not represent any change in
performance/functionality.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>