TI DaVinci: DM355: Config Cleanup and Update

TI DaVinci: DM355: Config Cleanup and Update

This patch does the following
1) Enables the NAND driver which is now available.
2) Enables the 'CONFIG_MTD_DEVICE' as without this the
compilation will fail
3) We now have a safe place to store environment and defines
an offset where this can be stored. This offset value is such that it is after
the location where U-Boot is flashed using TI flash utilities.
4) Enables Bootdelay
5) Increases malloc() arena size. Manufacturers are coming out with
NAND with large blocks sizes of upto 1 MiB. It has been noticed that
as the block size of the NAND used is increased, if this particular
value is not increased, the NAND driver will output out of memory
errors.

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>