mtd: mxc_nand: fix 2KiB pagesize NAND on i.MX27

This patch allows i.MX27 to support 2KiB pagesize NAND flash.
We are using a 1.8V NAND flash which datasheet (unfortunately only
available under NDA) says :
Page size: x8: 2,112 bytes (2,048 + 64 bytes).
Without this patch, all sectors are marked as bad eraseblock.

Signed-off-by: Eric Benard <ebenard@eukrea.com>
Acked-by : Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>