imx: gpmi: add defines for hw randominizer

Extend GPMI Integrated ECC Control Register Description, include
additional defines for enabling randomizer function and providing
proper randomizer type.

For additional details check i.MX7 APR, section
9.6.6.3 GPMI Integrated ECC Control Register Description
(GPMI_ECCCTRLn)

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Tested-by: Max Krummenacher <max.krummenacher@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>