treewide: fix board identifier in overlays for lpcxpresso55s69

Fix board identifier in overlays for the lpcxpresso55s69_cpu0 target.
Board identifiers were renamed with the following command:

for file in $(find . -name "lpcxpresso55s69_cpu0.*"); do;
	mv $file ${file/_cpu0/_lpc55s69_cpu0};
done

Additionally, remove lpcxpresso55s69_ns overlay targets where they are
no longer needed (or rename them where they are)

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>