ARMv8/layerscape: Add FSL PPA support

The FSL Primary Protected Application (PPA) is a software component
loaded during boot which runs in TrustZone and remains resident
after boot.

Use the secure firmware framework to integrate FSL PPA into U-Boot.

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