ARMv8/Layerscape: switch SMP method accordingly

If the PSCI and PPA is ready, skip the fixup for spin-table and
waking secondary cores. Otherwise, change SMP method to spin-table,
and the device node of PSCI will be removed.

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