mtd: nand: vf610_nfc: add hardware BCH-ECC support

This adds hardware ECC support using the BCH encoder in the NFC IP.
The ECC encoder supports up to 32-bit correction by using 60 error
correction bytes. There is no sub-page ECC step, ECC is calculated
always across the whole page (up to 2k pages).

Limitations:
- HW ECC: Only 2K page with 64+ OOB.
- HW ECC: Only 24 and 32-bit error correction implemented.

Raw writes have been tested using the generic nand_write_page_raw
implementation. However, raw reads are currently not possible
because the controller need to know whether we are going to use
the ECC mode already at NAND_CMD_READ0 command time. At this point
we do not have the information whether it is a raw read or a
regular read at driver level...

Signed-off-by: Bill Pringlemeir <bpringlemeir@nbsps.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>