* gnu/bootloader.scm (menu-entry-device-mount-point): New variable. Export it.
(<menu-entry>: New field "device".
* gnu/bootloader/grub.scm (grub-confgiuration-file): Handle <menu-entry>
entries.
* gnu/bootloader/extlinux.scm (extlinux-configuration-file): Handle
<menu-entry> entries.
* gnu/system.scm (menu->entry->boot-parameters): Delete variable.
(boot-parameters->menu-entry): New variable. Export it.
(operating-system-bootcfg): Make OLD-ENTRIES a list of <menu-entry>.
* guix/script/system.scm (reinstall-bootloader): Fix bootcfg usage.
(perform-action): Fix bootcfg usage.
* gnu/bootloader.scm (<menu-entry>): New variable. Export associated getters,
This record is extracted from grub module.
* gnu/bootloader/extlinux.scm (extlinux-configuration-file): Use
menu-entry->boot-parameters to convert menu-entry records to
boot-parameters.
* gnu/bootloader/grub.scm (<menu-entry>): Remove.
(boot-parameters->menu-entry): Remove.
(grub-configuration-file): Use boot-parameters to create configuration
entries.
* gnu/system.scm (menu-entry->boot-parameters): New exported procedure.
* gnu/bootloader.scm: New file.
* gnu/bootloader/extlinux.scm: New file.
* gnu/bootloader/grub.scm: New file.
* gnu/local.mk: Build new files.
* gnu/system.scm: Adapt to new bootloader api.
* gnu/scripts/system.scm: Adapt to new bootloader api.
* gnu.scm: Remove (gnu system grub) and replace by (gnu bootloader) and (gnu
bootloader grub) modules.
* gnu/system/grub.scm: Moved content to gnu/bootloader/grub.scm.
* gnu/system/vm: Replace (gnu system grub) module by (gnu bootloader).
* gnu/tests.scm: Ditto.
* gnu/tests/nfs.scm: Ditto.
