kmod: Beef up firmware symlink chasing

kmod: Beef up firmware symlink chasing

- It turns out we need to handle absolutely symlinks after all as
  /usr/lib/firmware/regulatory.db is a symlink to /etc/alternatives
  in Debian and derivatives.
- Our previous implementation didn't handle cases where a symlink target
  consisted out of two parts e.g. if C -> A/B then we wouldn't try to resolve
  A.

Fix both issues by switching to a minimal implementation of the chase()
function in systemd.

To avoid having to include /etc stuff in the kernel modules initrd, we resolve
get rid of any intermediate symlinks to /etc/alternatives that we encounter.

Follow up for 221293e33defe30b111bc13957a0d52d2ea1c45b