mtd: gpmi: set the Golois Field bit for mx6q's BCH

The GF13 can be only used in the following case:
    The ECC data chunk is less then 1K bytes.

In mx23/mx28, the ecc data chunk is 512 bytes. So it is okay.

But in mx6q, we begin to use some large nand chip whose ecc
data chunk maybe 1K bytes long.  So when the data chunk is 1K bytes,
we have to use the GF14.

This patch sets the Golois Field bit when the GF14 is needed.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>