mtd: nand: Sync with Linux v4.6

Updates the NAND code to match Linux v4.6. The previous sync was from
Linux v4.1 in commit d3963721d93fafa.

Note that none of the individual NAND drivers tracked Linux closely
enough to be synced themselves, other than manually applying a few
cross-tree changes.

Signed-off-by: Scott Wood <oss@buserror.net>
Tested-by: Heiko Schocher <hs@denx.de>

nand: Merge BCH code from Linux nand driver

[backport from linux commit 02f8c6aee8df3cdc935e9bdd4f2d020306035dbe]

This patch merges the BCH ECC algorithm from the 3.0 Linux kernel.
This enables U-Boot to support modern NAND flash chips that
require more than 1-bit of ECC in software.

Signed-off-by: Christian Hitz <christian.hitz@aizo.com>
Cc: Scott Wood <scottwood@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>