snippets: Support nordic-ppr and nordic-ppr-xip on nRF92

Add overlays for booting PPR on the `nrf9280pdk/nrf9280/cpuapp` target.
They are identical to the nRF54H ones because of similar DT structure.

Signed-off-by: Grzegorz Swiderski <grzegorz.swiderski@nordicsemi.no>