ARMv8/fsl-layerscape: Correct the OCRAM size

The real size of OCRAM is 128KiB, so correct the size of OCRAM.
And OCRAM reserved 2MiB space, then add a new macro to describe
it, which is used for MMU setup.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>