qemu: Match firmware with fully resolved and canonicalized paths

qemu: Match firmware with fully resolved and canonicalized paths

Distros may provide compatibility symlinks after moving firmware files
around, but they won't work for existing VMs when doing a straight
string comparison.

I tried to compare inodes instead, but even glib doesn't provide a
straightforward cross-platform method to do this.

Resolves: https://bugs.gentoo.org/960591
Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>