osdep/linux: handle autofs entries in /proc/self/mountinfo

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