mtd: rawnand: toshiba: Add support for Toshiba Memory BENAND (Built-in ECC NAND)

This patch is a patch to support TOSHIBA MEMORY CORPORATION BENAND
memory devices.  Check the status of the built-in ECC with the Read
Status command without using the vendor specific command.  The Read
Status command only knows whether there was bitflips above the
threshold and can not get accurate bitflips.  For now, I set
max_bitflips mtd->bitflip_threshold.

Signed-off-by: KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>