Not just mkknlimg - the entire preinst and postinst scripts in the rbp2-image package are written in perl, so anything corrupt with the perl installation is going to cause the kernel package to fail to install. I can’t think of any other system packages off hand whose preinst and postinst are written in perl so that’s why nothing else failed.
You could try doing a forced reinstall of perl, but if the underlying cause is file system corruption then it may only be a band aid fix or may actually make things worse:
sudo apt-get install perl perl-base perl-modules --reinstall
Afterwards try the following:
sudo apt-get update
sudo dkpg --configure -a
sudo apt-get -f dist-upgrade