omap3: overo: Use software BCH8 ECC for NAND

Overo COMs have NAND flash that requires 4-bit ECC or better except for
the first sector which can use 1-bit ECC.  The boot ROM expects to load
a payload from NAND written using 1-bit hardware-based ECC.  In short,
write SPL to NAND something like this (4 times for redundancy):
 #> nandecc hw
 #> nand write ${loadaddr} 0x0 ${filesize}
 #> nand write ${loadaddr} 0x20000 ${filesize}
 #> nand write ${loadaddr} 0x40000 ${filesize}
 #> nand write ${loadaddr} 0x60000 ${filesize}

Then, switch back to software-based BCH8 for everything else:
 #> nandecc sw bch8

After [1], enlarge the max size of the SPL so the BCH code can fit.

[1] https://www.mail-archive.com/u-boot@lists.denx.de/msg163912.html



Signed-off-by: Ash Charles <ashcharles@gmail.com>