osdep/linux: handle autofs entries in /proc/self/mountinfo
    
    These entries have placeholder for device name and so are useless for our
    purpose. grub failed with something like
    
    grub-install: error: failed to get canonical path of `systemd-1'.
    
    When we see autofs entry, record it (to keep parent-child relationship) but
    continue to look for real mount. If it is found, we process it as usual. If
    only autofs entry exists, attempt to trigger mount by opening mount point
    and retry. Mount point itself is then kept open to avoid timeout.
    
    Recent systemd is by default using automount for /boot/efi so this should
    become more popular problem on EFI systems.
    
    Closes: 49942