davinci_nand: cleanup II (CONFIG_SYS_DAVINCI_BROKEN_ECC)

Remove CONFIG_SYS_DAVINCI_BROKEN_ECC option.  It's not just nasty;
it's also unused by any current boards, and doesn't even match the
main U-Boot distributions from TI (which use soft ECC, or 4-bit ECC
on newer chips that support it).

DaVinci GIT kernels since 2.6.24, and mainline Linux since 2.6.30,
match non-BROKEN code paths for 1-bit HW ECC.  The BROKEN code paths
do seem to partially match what MontaVista/TI kernels (4.0/2.6.10,
and 5.0/2.6.18) do ... but only for small pages.  Large page support
is really broken (and it's unclear just what software it was trying
to match!), and the ECC layout was making three more bytes available
for use by filesystem (or whatever) code.

Since this option itself seems broken, remove it.  Add a comment
about the MV/TI compat issue, and the most straightforward way to
address it (should someone really need to solve it).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Scott Wood <scottwood@freescale.com>