The "Primary Protected Application" (PPA) is a PSCI compliant firmware
distributed by NXP. It is needed to start the secondary cores on
Layerscape SoCs. Without it Linux will be started in EL3 and doesn't
work properly. The precompiled firmware images can be found on
https://github.com/NXP/qoriq-ppa-binary and are not included in
barebox.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>