configs: layerscape: delete defconfigs using legacy PPA secure FW

PPA was a secure firmware developed in-house which is no longer
supported and replaced by TF-A quite some years ago. This makes
the defconfigs that make use of PPA obsolete, so remove them.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
 [Merged part 1 and part 2]
Signed-off-by: Peng Fan <peng.fan@nxp.com>