Add support for KARO TX25 board

This is an i.MX25 base board with only NAND
so it uses nand_spl to boot.

Signed-off-by: John Rigby <jcrigby@gmail.com>

Tune configuration, add support for (redundant) environment in NAND.
Signed-off-by: Wolfgang Denk <wd@denx.de>

Acked-by: Wolfgang Denk <wd@denx.de>
CC: Fred Fan <fanyefeng@gmail.com>
CC: Tom <Tom.Rix@windriver.com>