Setup NAND flash timing on DM6467T EVM.

Without the timing setup, the NAND flash on DM6467T
RevC EVM reports a number of random bad blocks because
of read errors.

Also, with this, copying a 100M file on RevB EVM takes
~35 sec against 1 minute 30 seconds earlier.
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>