Revert "nand: make 1-bit software ECC configurable"

This reverts commit 4fee6c2f.

It breaks boards that currently rely on soft-ecc, as pointed out here:
http://patchwork.ozlabs.org/patch/140872/



The reverted patch should be resubmitted with documentation, and with the
CONFIG_MTD_ECC_SOFT selected from every board that needs it.  We could
start by looking at what NAND driver the board selects, and whether
that driver ever asks for soft ECC.

Signed-off-by: Scott Wood <scottwood@freescale.com>