On systems where /boot is msdosfs (such as powernv ppc64), we are normally mounting the /boot filesystem separately from /.

Since msdosfs also cannot support symlinks, we cannot work around this by having a symlink /boot/boot => /boot/. either.

So, in the case where a file is not found when loading a file from msdosfs in libsa, if the path started with /boot/, try again without that path component.

(Noticed while working on petitboot loader.)