Improve grub-mkconfig performance when there are several menu
entries on a single filesystem.
* util/grub.d/10_linux.in (linux_entry): Cache the output of
prepare_grub_to_access_device.
* util/grub.d/10_kfreebsd.in (kfreebsd_entry): Likewise.
* util/grub.d/30_os-prober.in: Likewise.
* util/grub.d/10_freebsd.in: Remove.
* util/grub.d/10_kfreebsd.in: New file (based on 10_linux.in).
* configure.ac: Set host_kernel=kfreebsd for FreeBSD and GNU/kFreeBSD.
* util/grub.d/10_freebsd.in: Remove.
* util/grub.d/10_kfreebsd.in: New file (based on 10_linux.in).
* configure.ac: Set host_kernel=kfreebsd for FreeBSD and GNU/kFreeBSD.