mtd: nand: fsl_ifc: Fix handling of bitflips in erased pages

mtd: nand: fsl_ifc: Fix handling of bitflips in erased pages

This is a fix made for the fsl_ifc_nand driver on linux kernel by
Pavel Machek and is applied to uboot. It is currently on applied on
linux-mtd.

https://patchwork.kernel.org/patch/9758117/

IFC always raises ECC errors on erased pages. It is only ignored when
the buffer is checked for all 0xFF by is_blank(). The problem is a
single bitflip will cause is_blank() and then mtd_read to fail. The fix
makes use of nand_check_erased_ecc_chunk() to check for empty pages
instead of is_blank(). This also makes sure that reads are made at ECC
page size granularity to get a proper bitflip count. If the number of
bitflips does not exceed the ECC strength, the page is considered empty
and the bitflips will be corrected when data is sent to the higher
layers (e.g. ubi).

Signed-off-by: Darwin Dingel <darwin.dingel@alliedtelesis.co.nz>
Cc: Pavel Machek <pavel@denx.de>
Cc: Scott Wood <oss@buserror.net>
Acked-by: Pavel Machek <pavel@denx.de>
[Kurt: Replaced dev_err by printf due to compiler warnings]
Tested-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: York Sun <york.sun@nxp.com>