systemd: change pni-names logic to something less confusing

systemd: change pni-names logic to something less confusing

Using bb.utils.contains in negative logic leads to either overly verbose
or plain confusing code, so harness the power of Ross and Antonin to
make this less verbose and slightly clearer.

This moves the negative logic from the inline python ('true if not') to
bash ('if !').

Signed-off-by: Koen Kooi <koen.kooi@oss.qualcomm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>