armv7/ls1021a: allow OCRAM access permission as R/W in SPL

On LS1021A Rev2.0, OCRAM's security level needs to be changed to
non-secure access for SD boot. This patch will allow OCRAM
access permission as R/W in SPL.

Signed-off-by: Alison Wang <alison.wang@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>