we already supported syslinux but not grub
support grub by scanning for the most common paths,
based on the most popular distros
we don't hardcode this with * because it slows down
the boot, and in practise many distros still use the
same grub.cfg location as in BIOS systems (the EFI
one is often just a link to the BIOS one)
Signed-off-by: Leah Rowe <leah@libreboot.org>